NEW 7" REELS OF • *. GI.dlOtape gIve you EXTRA VALUE at no ·extra cost!
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SPLIT-SECOND TIMING with New 2%:" Hub Timing errors are virtually eliminated by this improved reel design which minimizes tensio n and speed changes throughout the winding cycle. Ratio of D.D. to hub diameter is the same as on the standard NAB aluminum reel.
PERFECTED ANTI- FRICTION With Audiotape, all of these extra-value features are standard. There's no extra cost - no problem of separate inventories or PROCESS. Reduces head wear-eliminates variations in tape quality. annoying tape "squeal" - prevents "tackiness" F or there's only one Audiotape - the fin est obtainable anywhere. even under extreme temperature and humidity Test it - compare it -let Audiotape speak for itself. conditions. The new 7-inch plastic reel with large diameter hub for greater timing accuracy is now being supplied on all orders unless other wise specified. Because of increased hub diameter, maximum reel MAXIMUM UNIFORMITY OF capacity is slightly over 1200 feet. Older style Audiotape reels 3 OUTPUT. All 7" and 10" reels of plastic· with 1 ,1,," hub and 1250 feet of tape will continue to be furnished on request at the same price. base Audiotape are guaranteed to have an out·, * Trade Mark put uniformity within ± lJ.. db - and reel-to· reel-variation of less than ± 1/2 db. What's more, there's an actual output curve in every S-reel package to prove it. AUDIO DEYICES, Inc. 444 Madison Ave., New York 22, N. Y. Export Department, 13 East 40th St., New York 16, N. Y., Cables "ARLAB" • aucliotape • • December
INCLUDINC House & Garden
Says • "Music In C. G. McProud, Editor and Publisher Harri e K. Richardson, Associate Editor Edgar M. Villchur, Contributin g Editor Luci Turner, Prp duction Manager S. L. Cahn, Advertising Director El izabeth Beebe, Circul ation Manager H. N. Reizes, Advertising Manager Life" Ed ar E. Newma Circulation Promoti on Director Ed itorial Advisory Board Representatives H. Thorpe Covington. Special Representative Howard A. Ch inn 677 N. Michigan Ave., Ch icago II , III . John D. Calvin Sanford R. Cowan. Mid-West Representati ve 67 W. 44th St., New York 18. N. Y. C. J. LeBel James C. Galloway. Pacific Coast Sales 816 W. 5th St., Los Angeles 17. Calif. J. p. Maxfield Technical Book & Magazine Co. 297 Swanston St., Melbourne. C. I. George M. Nixon Victoria. Australia CONTENTS OCTOBER, 1952 Vo l. 36, No. 10 Audio Patents- Richard H. Der! ...... 2 Letters ...... 6 London Letter- Leollard Card'u,ner ...... 12 Book Reviews ...... 17 Says it l!!.. a big 24 page portfolio Editor's Report ...... 18 Intermodulation Distortion- Richard C. H itchcock ...... 21 packed with news and information A Critical Feedback Analysis- Harold Klimpel ...... 23 Stereophonic Reproduction- James Moil' ...... 26 on every phase of Music .' . . Design for Clean Bass- Edwa1'd J. Gately, h...... 29 P lanning & Building a Radio Studio-Part 5- Eugene F. Co1'iell ...... 30 including feat ure articles A Corner-Mounting Infinite Baffie-M. V. Kiebe1't, h ...... 32 The Vio l in~Pa1't 2- Alb'ert Preisrnan ...... 34 on Tape Recorders, and H andbook of Sound Reproduction-Chapter 5- E . M. Villchlw . .. " ...... 36 High Fidelity. ~~~~':~~n~~ri;:~~e:~e~~ ' sic~ioN ' ... i ' ...... 38 No Coded Signals- H. S . Mor1'·is ...... 40 Convention Progran1 ...... 58 • Says it l.2. an important audience of Employment Register ...... 83 influential readers who have the means to Record Revue-Edward Tatnal:l Ca,nby ...... 46 Tape Recorder Echo Effects- R. S. Houston ...... 52 buy the best in mcUsical recording. Audio Fair Story ...... 58 New Products ...... 62 • Says it .!£. your £fe alers in a special Some Pickup Design Considerations-Po G'. A . H. Voigt ...... 64 promotion package complete with ideas Some Observations on Demonstration Technique- Harrie K. Richa1'dson . . . 84 New Literature ...... 87 of how to increase business in Music {o r Price and Product Changes- Radio Master's Report ...... 94 Christmas with House & Garden tie-ins. Industry Notes ...... 95 Advertising Index ...... 96 • House & Gardm's December Music COVER Issue is quite evidently an ideal issue to Two prominent figures in the audio world combine to make this photograph one of the more newsworthy to grace }E's cover in many 1110nths. At the left is Mr. tzme in on. Music advertising in the issue Earl M. Johnson, newly-elected vice-president in ' charge of engineering and will be thoroug'hly merchandised. Tell station relations for Mutual Broadcasting System. On the right is Mr. R. your dealers to use the -issue itself as a Stahl, president of Ectro, Inc., Delaware, Ohio, explaining the design and operation of the new battery-operated Cub Corder tape recorder. selling mamtal ... as a part of holiday Mr. Stahl- who, incidentally, flew to New York solely for this displays. picture- made news of national impact recently when', as founder and president of Ciro, Inc., he ~o l d !uanufacturing rights for • Closing date fo r your the Ciroflex camera to Graflex Corporation, in order to de vote his future activities to the expanding field of tape advertisement in the December !·ecording. (Photo by Nemeth) M usic Issue is OCTOBER 15th. RADIO MAGAZINES, INC., P. O. BOX 629, MINEOLA, N. Y. AUDIO ENGINEERING (title registered U. S. Pat. OIT.) is published monthly at 10 McGovern Avenue. Lancaster. Po .• by Radio Magazln ... IDC .• Henry A. Scbober. President; C. G. McProud. Secretary. Executive and Editorial Offices: 20~ Front St .• Mineola. N. Y. Subscription rates-United Stat... U. S. Possessions and Can ad •• $3.00 for 1 year. $5.00 for 2 years; ellewbere $4.00 per year. Single copies 35c. Prlnted In U. S. A. All rights reserved. Entire contents House & Garden copyriebt 1952 by Radio Magazines, Inc. Entered as Second Class Matter February 9, 1950. at the Post Office. Lan· caster. Pa. under the Act of Marcb 3. 1879. 420 L exi~glon Avenue. New York 17. New York
AUDIO ENGINEERING • OCTOBER, 1~52 NEW! • • ~l]1lDUCJ) • The turntable • • that YJll! helped • • • us design! [p~U'm!l~~
RICHARD H. DORP
IVO POWER-AMPLIFIER CIRCUITS invented A (using the convention more common to , by Harry W. Becker of Chicago pro electronics that current flow and electron vide interesting possibilities for achiev How are identical) from plate to power ing high output and low distortion together supply. A t the same time the cathode cur with rather unusual economy of materials rent flows downward through winding B and size. from ground to cathode. The two windings The first is a single-tube output stage are thus in series aiding, with inverse volt with, according to the inventor, the advan age drop relations with respect to g round. tages of push-pull, negative feedback, and The latter is so because actual ground is low source impedance normally present only connected to the end of winding B nearest in much more elaborate circuits. The patent the center of the primary and a.c. ground is numbered 2,595,443 and the schematic is (we assume the power supply is conven REK-O-KUT shown in Fig. 1. tionally bypassed by its filte r ) is connected 3-SPEED, 16" The principal "gimmick" here is an out to the end of winding A nearest the center. put transformer with two primary windings T his is the same condition as occurs in an Transcription Turntable and extremely simple but ingenious cir ordinary push-pull stage. \;Yinding B, however, is the load element FOR BROADCAST AND cuitry in connection with it. T,he tube is a beam tetrode-pet'haps a 6L6 or something of a cathode follower. As such, the voltage RECORDING STUDIOS similar. The high end of the input signal is across it is in phase with the input voltage connected to the grid through blocking and the net voltage across it is the dif capacitor Ct in the usual manner and the ferential. The resulting feedback tends to other end of the input source may be reduce di stortion, as in any cathode fo l THE new B-16H three-speed, 16" tran ?,rounded. The lower end of grid-leak R" lower, and increase the effective input im scription turntable is not a modifica IS connected to the lower end of cathode pedance of the stage. Because of the mag tion of a two-speed machine, but a bias resistor R ., which is bypassed in the netic coupling with the plate winding A, c?mpletely new design, with opera usual way by C• . The junction of the two noise and distortion generated within the tIOnal controls suggested by leading resistors is not connected directly to ground, stage itself is reduced even further. engineers. Now you can play all three however, but through winding B of the So far the amplifier should give good re speeds-33'/3, 78 and the popular 45 transformer. Winding B is thus the load sults with enough excitation to produce -with equal facility. element of a conventional cathode-fo llower rated output. The output may be increased of the type in which the grid leak is usually well above normal rating, however, with The B-16H can be quickly and easily connected to a tap on a cathode res istor. out increase in distortion because of the fitted into your present 2-speed tran· s€reen current. Screen current is, as usual, scription consoles or cabinets. The base out of phase with plate current; that is, is drilled and tapped for mounting B+ when the grid goes positive and plate cur Audak, Grey or Pickering arms. Main· rent increases, screen current decreases. tenance is simple .. . turntable, motor The a.c. component of the screen current pulley and idlers are easily accessible. passes through Ct, through winding B, to the cathode (through the . bias bypass OUTSTANDING FEATURES: capacitor). Passing through winding B in 45. RPM Adapter ... disappearing type, built INPUT opposite phase to the plate portion of the Into hub of turntable. cathode current, it is sufficient to cancel the Aluminum Base ... square shape, radial ribbed distorted portion of the plate current. for utmost rigidity. As an additional bonus, winding B is Speed Changes . .. instantaneous for all three connected to a low-impedance source (the speeds-contpolled by selector. tube cathode) and provides a high damping Speed Shift .. . Mastermatic, self·locking. A factor on the loudspeaker load connected REK-O·KUT exclusive. to the transfQrmer secondary, thus reducing Speed Variation . .. Meets the NAB. standard the distortion normally resulting from the for speed variation and "wow" content. use of tubes with high plate impedance. Turntable .•. 16" cast aluminum, lathe turned, = Used as a power amplifier there would with extra heavy rim for balanced flywheel probably be no' voltag-e gain, especially if action. Sub-mounted in base. Fig. 1. these wil1dings A and B were identical. The Motor ... Hysteresis Synchronous. 60 cycles in ventor points out, however, that the cir AC , 115 volts. Available in other frequencies and voltages at extra cost. At the same time winding A is used as cuit can be used for a voltage amplifier if the load element for- the plate in the stand winding A is given a larger number of Dimensions .. . 11/2" above base. 6" below. 20" wide x 183/,'" deep. Shipping weight. ard manner. The screen is simply connected turns than winding B. The voltage amplifier 30 Ib ~. to the B-plus line and is bypassed to ground' would retain the advantages of simulated in the usual way by capacitor C,. As it push-pull operation and negative feedback. MODEL B-16H • . ...•.. $250.00 net. stands, then, we have a stage acting simul What the actual relative number of turns , Available at Leading Radio Parts taneously as a ca,thode follower and as a is when the circuit is used as a power Distributors. Write lor detailed literatllre. plate-loaded amplifi er, with the outstanding amplifier is not stated, but the language of departure from the norm that the load ele the patent specification leads the writer ments are also coupled to each other mag to believe them identical, which means that REK-O-KUT CO. netically. a conventional split-primary transformer Forgetting for the moment about screen could be used. 38-01 Queens Blvd., long Island City, N. Y. · current-when the grid goes positive, plate EXPORT DIVISION, 458 Broadway, N. Y. C. U.S .A. Canada: Atlas Radio (orp., ltd., Toronto 28, 0(1'. curren t flows downwall'~ through 'W'i~ding Double Push-Pull System * 255 W. 84th' St., Ne~rJ York 24, N . Y The second Becker patent, No. 2,595,444,
2 AUDIO ENGINEERING • OCTOBER, 1952 SILECTRON He" CORES fOr?..I//~ e:leH~ IN PRODUCTION QUANTITIES
II • • • wound from strip as thin 'as 0.0002S I
Nowavailable-"C" Cores made sion, and careful processing of these from Silectron (oriented silicon joints eliminates short-circuiting of steel) thin-gauge strip to the the laminations. highest standards of quality. Cores with "RIBBED CON· Arnold is now producing these STRUCTION"* can be supplied cor~s in a full range of sizes wound where desirable. from %, 1f2, 1, 2 and 4-mil strip, Ultra thin-gauge oriel;lted silicon * Arnold "C" Cores are made to highly exacting standards of qual also 29-gauge strip, with the entire steel strip for Arnold "c" Cores is ity and -uniformity. Physical di output scheduled for end use by the rolled in our own plant on our new mensions are held to close toler ances, and each core is tested as U. S. Government. The oriented micro-gauge 20-high Sendzimir follows: silicon steel strip from which they cold-rolling mill. For the cores in * 29-gauge Silectron cut cores are are wound is made to a tolerance of current production, standard tests tested for watt loss and excitation plus nothing and minus mill toler are conducted as noted in the 'box volt-amperes at 60 cycles, at a peak flux density of 15 kg. ance, to assure designers and users at left-and special electrical tests of the lowest core losses and the may be made to meet specific * 4-mil cores are tested for watt loss and excitation volt-amperes at 400 highest quality in the respective operating conditions. cycles, at a peak flux density of 15 kg. / gauges. Butt joints are accurately made to a high standard of preci- • We invite your inquiries. -* 2-mil cores are tested for pulse permeability at 2 microseconds, 400 pulses per second, at a peak *Manufactured under license arrangements with Westinghouse Electric Corp. wao 4 2 11 flux density of 10 kg. * I-mil cores are tested for pulse permeahility at 0.25 microseconds, 1000 pulses per second, at a peak flux density of 2500 gauss. *' '/2 and '/.-mil core tests by special arrangement with the customer.
AUDIO ENGINEERING • OCTOBER, 1952 3 consolidates the gaips of the first and par lays them into a double push-pull circuit in which two tubes do the work of four. The circuit, shown in Fig. 2, gives the details. The grids of the tubes are excited by the output of any standard phase splitter in the usual way. Consider first V, and its connections, looking for cross-reference at Fig. 1. Windings A and B of the output transformer correspond in the two figures. Examination shows that if V, and its cir cuits, along with windings A' and B' were eliminated, the remaining components and connections would be identical to Fig. 1. N ow the inventor adds two more windings, A' and B/, together with tube V.-the cir curity of which is identical to that of V, and excites the grids out of phase. The result is, of C0urse, the same as in Fig. 1 but twice as much of it, plus, for the Thomases who doubted the possibility of real balance in the early circuit, assuage 'ew. ment of their doubts, for the later idea is certainly genuine push-pull. And, says the inventor, the power delivered by two tubes in · this circuit at a given distortion (the actual phraseology of the patent uses the word "undistorted," about as vague as exists in audio today) is approximately twice what the same tubes would deliver The TURNER 51D in a conventional push-pull amplifier! The new Turner Model 5ID (similar B+ to the Model 50 Aristocrat) offers ex ceptionally high quality performance at a new low cost. The Model 5ID is essentially non directional in operation - equally effective for individual or group pickups. A unique ball swivel coupler permits fast change from stand to hand or vice versa. Use the Model 5ID anywhere, indoors or out - it's blast proof, and not affected by variations in humidity or tem perature. Advanced circuit design with high output dy namic generator requires no closely associated auxiliary equipment for outstanding results. For TV, FM, AM, recording and public address specify the Turner Model 5ID - the outstanding dynamic micro phone in its field. SPECIFICATIONS Frequency Response: 60 to 13,000 c.p.s. substantially flat. Output Level: 58 db below 1 volt/dyne/ sq. cm. at high impedance. Impedance: Choice of 50, 200 or 500 ohms connected for bal- anced line output; high impedance (25,000 ohms) connected for single ended output. Polar Pattern: Essentially non-directional in any position. Transformer: Magnetically shielded for minimum hum pickup. Diaphragm: Special aluminum alloy. Fig. 2. Case: All metal rich umber grey finish. A.F.e. Discriminator Mounting: Boll and swivel type, tilts in any direction. Standard There are few complaints the writer has %" - 27 thread. heard more from both lay audio fans and Dimensions: 1 %" maximum diameter, 6V2" long (less cable con technical personnel than those concerning nector). FM tuner drift, especially on weak stations. Weight: 16 oz. (less coble). There are, of course, tuners now with Cable: 12 foot high quolity two conductor shielded coble with a. f. c. but many an old tuner can fai rly Cannon quick-disconnect plug. easily be converted to automatic frequency control. The satisfying result is that you List Price: $85.00. tune somewhere near a station and suddenly it drops into place; no more delicate tuning for the exact center and no more getting up every ten minutes to retune. Clyde J. Nor ton has invented an a. f. c. discriminator which is simple but accurate, and is effec tive over a good deal wider deviation range than usual. The patent, assigned' to Syl vania, is No. 2,581,968, and the circuit is 929 17th St. N. E. diagrammed in Fig. 3. • Cedar ~apids, Iowa LrC, and L ,-C, are a pair of series IN CANADA: EXPORT resonant circuits connected in parallel with Canadian Marconi Co., Ltd. Ad. Auriema, Inc. each other and across a source of r. f. Toronto, Ont., & Branches 89 Brood Street," New York 4 [Continued on page 68J
4 AUDIO ENGINEERING • OCTOBER, 1952 Whether for video or standard broadcasting, Engineers, with an eye to the future, will appreciate the exceptional versatility of GATES Speech Input Equipment. Here is equipment with unusual adaptability to the ever-changing . demands of programming techniques. If you are planning a studio'installation today - think of tomorrow, and con sider the flexibility, the expandability of GATES Speech Input Equipment. Space prevents fully describing the circuit handling capa bilities of the three consoles shown. Y6u are invited to write for the GATES SPEECH INPUT CATALOG where functional block diagrams and additional data will better acquaint you with these versatile GATES Consoles - truly, Speech Input Equipment With A Future.
Ideally suited for small station studio applications or as par,t of larger master control type installation, the GATES 52-CS StudioeUe has all of the necessary facilities for complete studio operation and will fulfill the most rigid requirements of fidelity, low noise and dis tortion. Facilities include four mixing channels. Two preamplifiers, one program amplifier and one monitoring amplifier plus complete power supply are self:contained. Send for GATES SPEECH INPUT CATALOG Today.
AUDIO ENGINEERING • OCTOBER, 1952 5 LETTERS for Oscillator Sir: Now and then an author proceeds from a soundly-reasoned base to theoretical con laboratory clusions which are so obviously true that he fails to check them against practice. Un fortunately, when theory and experimental and fact are in collision, it is theory that must be revised. We fear that Dunford A. Kelly, in the August issue, has made this unhappy mis switchboard take. Referring to the SMPTE intermodu lation test, he reasons that "Thus the re Here are a few examples of Cannon's Experimental sults do not correspond to audible distor Laboratory and Switchboard Connectors. They are tion." We are sorry to have to point out . used extensively throughout industry, public utilities, that the motion picture industry, through many listening tests, showed about fifteen sound studios, broadcasting stations, college and uni years ago that the SMPTE intermodula versity physics and chemistry laboratories, in AC net tion test results do correlate with aural work analyzers and ele~tronic analog computers. They judgements of distortion. They have, there may be applied wherever quick disconnect switching fore; continued to rely on this method for CSR Tandem Receptacle system and equipment tests. CSP Plug We note, also, that he has fallen into the pitfall of believing that "predictable ratios correlate harmonic and intermodulation levels." While this is true in some cases, in most cases it is simply not so. As a single example, consider an amplifier which consists of a wide-band non-linear first stage followed by a linear low-pass second stage which cuts off sharply at 15,000 cps. Harmonic analysis will indicate that the system generates no harmonics. when the input frequency is above 7,500 cps, and that it generates no harmonics other than the second when the input frequency is be tween 5,000 and 7,500 cps. Intermodulation tests, however, when properly applied, will indicate non-linearity of all orders for fre quencies nearly up to· the cutoff point. It is SWPR·4 Switching Plug having both clear, therefore, that any correlation be pin and sockel contacts SDR Receptacle tween the results of the various distortion t~sts must .depend strongly on the frequen and patch cord plugs are required. High grade ma cies at which the tests are carried out. terials are used throughout. Molded phenolic of high Aside from our criticisms, we wish to congratulate Mr. Kelly on an excellent dielectric strength is used for insulation. Both pin a nd piece of design work. socket contacts are machined from solid brass. Some C. J. LeBel, are silver plated. All are rated at 75 amps. Pin contacts Audio Instrument Company, Inc. are split for low loss seating in tapered bore sockets. 133 w. 14th St. Single contact fittings are supplied in either red or New York 11, N. Y. black phenolic to designate direct or alternating cur AMPLIFIER rent circuits respectively. Two-contact and larger plugs Sir: SR Receptacle have sand-blasted cast aluminum shells and handles Since publication of my article on the with clear lacquer finish. Various combinations of pin "Williamson Up To Date," I've received a and socket contacts are used ·as a polarizing guide. For consi.derable amount of correspondence further information write for Bulletin LS5-1951. relative to other transformers and circuit modifications. Accordingly, I believe it may be desirable to supply a few additional de SCR Plug tails in order to help answer these ques tions for all interested readers. As for transformers, the one specified was used originally because it is satisfac tory, and I had one immediately available. SCP Plug The output transformer in the 100-watt am plifiers mentioned ,was built by Freed, and the characteristics and performance are SRB Receptacle outstanding. Many other excellent units are available, and suitable performance should be expected from any of the better-quality lines. CANNON ELECTRIC Several manufacturers supply excellent non-inductive wire-wound resistors. Two watt composition units are really quite Since 1915 • good, and it is likely that use of such units in a power amplifier would not cause any Factories in Los Angeles, Toronto, New Haven, Benton difficulty. Harbor. Representatives in principal cities. Address in Recent discussions on the Williamson quiries to Cannon Electric Company, Dept. ]-109, P. o. amplifier have indicated a potential increase Box 75, Lincoln Heights Station, Los Angeles 31, Calif. in output with reduced IM when a tapped
6 AUDIO ENGINEERING • OCTOBER, 1952 portable accurate urvey lnexpensive eter easily operated
Locating "dead spots" with Sound Survey ~Meter . Assistant ~Mr. Warren Jenkins, Sound Engineer at Radio City Music Hall, repositions speakers to improve coverage. checks performance of sound reinforcement system at this theatre. The G-R Type 1555-A Sound Survey Meter saves time and improves quality of sound system installations at plants, offices, theatres, halls, churches, public buildings, schoolyards and playgrounds, recreation centers and outdoor gatherings. G-R Type 1555-A Sound Survey Meter con sists of a microphone, a calibrated This handy, versatile instrument simply and accurately measures the intensity of sound at any given point. It is very useful for both attenuator, an amplifier, an indicating the measurement of background noise preliminary to public address, meter, a nd weighting networks. theatre or high fidelity system installation, and for checking the level * Continuous level control and large panel of reproduced sound from such systems. By simply passing oscillator meter permit reading at a glance test tones or recorded voice through the amplifier-speaker system and noting the Sound Survey Meter indication at various locations, * Fits in trousers pocket; dimensions are the installer can readily: 6 x 3Ys x 231 inches Weighs only 1 lb., 14 oz. with batteries * Set volume to override background noises and cover all of * desired ·area. * Can be operated on a bench, tripod, or in hand by anyone * Locate speakers to eliminate "dead spots". * R ange is from 40 to 136 db above * Determine adequate system frequency response for the standard reference level particular sound-music, voice or ·other-to be amplified. * Three frequency characteristics approx The Sound Survey Meter also finds wide use for determining imate response of the ear at 40 db, sound levels of appliances, machinery and office equipment, for 70 db, and levels above 85 db. Uniform measuring acoustic reference levels when recording, and response response to all frequencies between 40 characteristics of loudspeakers and rooms, and for preliminary checks and 8,000 cycles also provided. to ascertain existence of noise levels harmful to hearing in factories and offices. TYPE 1555·A Sound Survey Meter ••• $125 TYPE 1555·P1 Leather Carrying Case. $10
AUDIO ENGINEERING • OCTOBER, 1952 7 transformer is used. The majority of circuits can be slightly im bere's \ proved by this means, but the gain may be offset by the reduc.ed damping that inevitably results when the screen-connected CIr cuit is used. Due to the inherent stability of the basic "up-to-date" circuit absolute reliability which employed adequate interstage decoupling and a power sup ply of relatively low impedance, ~he screen ~o~nection m~y. be made readily without the necessity of modlfymg the onglllal feedback-loop components or the interstage coupling circuits. Note that 40-l-Lf electronic capacitors were used in lieu of the for heavy duty original lO-l-Lf units. The use of paper units in this application is not practicable. Tests were made by connecting the screens to the Peerless transformer taps as suggested in the Sarser-Sprinkle article audio (JE, July 1952). It was found that at a 26-watt level, inclusion of the 100-ohm resistors in the circuit dropped the 1M from 8 per cent to 7 per cent. (The screen impedance and voltage drop ping action of the series resistor apparently provide a more amplification nearly correct voltage ratio on the screens.) The use of an 80-Jl.f ca~ode bypass capacitor on the 807's dropped the 1M from 16 per cent to 9.5 per cent at a 27-watt level, but had no measurable effect at power levels below 12 watts. A 300-l-lf capacitor provided a bit better performance at low frequencies. Use of the 12A Y7 and 5687 stages with the components speci fied in the "Up-to-Date" amplifier is entirely practicable with the Ultra-Linear output circuit, and the general design prin ciples are, of course, suitable for any similar power amplifier. The feedback loop should use the greater amount of feedback as shown in the ,writer's article, and for minimum distortion and maximum output should use the 250-ohm bias resistor in lieu of the 300-ohm unit shown in the Ultra-Linear modification in the July issue. Almost any desired pair of output tubes-807's, 5881's, 1625's, . or KT-66's-may be used with but negligible difference in per formance. The use of d.c. on power amplifier heaters is not ap parently necessary, and no measurable improvement is effected.
M. V. Kiebert, Jr., Ecli pse- Pio neer Division, Bendix Avi ation Corporation, Teterboro, N . J.
Tuners Sir: Recent letters to the Editor have touched upon the poor qual ity of transmission from FM stations and the poor state of re pair of FM sets as a probable reason for the less-than-satisfac tory FM reception too frequently encountered. Dismissing for the moment the special problems of fringe-area transmission and reception, it seems to me that both of the FM ,faults alluded to above flourish even in places where they have no business to be found-namely, in and around large cities. To begin with, many FM tuners are in a poor state of re pair because they are primarily products of impoverished de If you've been looking for an audio output tube that's stable sign (electrical and mechanical), and built to low or no stand under the most severe conditions-completely de pe ndable ards. In contrast to the several superb amplifiers that are avail able at reasonable prices, and the host of creditable or satisfac then this is it ! The Tung-Sol 5881 is rugged both mechanically and tory ones that are available at lesser cost, there is only one su electrically-and directly interchangeable with th e 6L6. perb FM tuner available at any price, and perhaps only two In creating the 5881, Tung-Sol engineers have made lavish use satisfactory ones in the $150 price range. Thel-e are available, however, any number of calibrated prox of the design and production techniques which have prove d th em imity fuses which fortuitously-certainly not by design-can selves over the past fifteen years-zirconium coating over the furnish an FM input signal of some sort, with the help of a carbonized metal plate and pure barium gette r to effectively subpoena. This electronic sow's ear is then required to be proc absorb gas for the life of the tube-g.old plate d wire to minimize essed into an acoustically silken purse. with inevitably disap pointing results. Mere iRspection reveals these "FM tuners" to grid emission. These are but a few of the major d esign improve be endowed with a haphazard physical layout reminiscent of an ments in the 588l. impromptu North African bazaar. Superimposed on this heap Tung-Sol produces the 5881 under laboratory conditions, to of poorly-shielded trash is a dial designed to take the place of a bank reference, ,which it never quite succeeds in doing. The assure peak efficiency and maximum uniformi ty. You'll fin d this whole is then studded with knobs that guarantee acceptance in tube has the stuff to take the whole range of audio service require an exclusive after-shave-lotion club. ments from protracted standby periods to repeated heavy over The plain fact is that the minds and hearts of those best quali loads. So, if absolute reliability is essential in your audio circuits, fied by training and personal standards to design and produce good r.f. equipment for the quality conscious have, since the war, the Tung-Sol 5881 is a "must." O rder it from your regular supplier. been devoted primarily to the improvement of the various audio Write for characteristics and performance data components of quality sound systems. Enough progress has been made, I believe, to justify a change in emphasis to permit r.f. to catch up with a.f. There is no reason, with the myriad TUNC-SOL ELECTRIC INC., NEWARK 4, N. J. engineering talents which exist within and without the frame Sales Off ices: Atlanta· Ch ica go· Cu lver Cit)' (Calif.) work of commercial organizations catering to the audio fra ternity-and despite the often-short-sighted and sometimes even Dallas · Denver· Detroit· Newa rk shabby attitudes of the management that employs them-,why Tu ng-Sol makes All -Glass Sealed Bea m Lamps, MInIature there should not be available on the market a mass-produced Lam ps, SIgn al Flashers, PIctu re Tubes, RadIo, TV and FM tuner in the $150 price class that possesses the following Special Purpose EI .ctron Tubes. among its attributes: 1. Stable circuits, effectively shielded; functions based upon less spectacular but more dependable tubes.
8 AUDIO ENGINEERING • OCTOBER, 1952 AUDIO ENGINEERING • OCTOBER, 1952 9 • 2. For large metropolitan areas, a model with crystal-controlled discontinuous tuning. 3. For fringe areas, a model with varia ble sensitivity and effective noise sup pression between stations; a tuning mechanism that does not depend on a piece of string. 4. Tuning controls that permit mounting in various positions on panel boards of various thicknesses; demountable gain controls and a.c. switch for in stallations where they are not needed. (Note the ascendancy of the pre-amp master control center.) S. Hardware and assembly that can withstand a 5-m.p.h. breeze with oc casional lO-m.p.h. gusts. It will be argued immediately by most manufacturing members of the "hi-fi" in dustry that what r want cannot be made to "retail" for $150 and yield a fair profit. Let me say that the cost of components and labor going into, say, a Williamson ampli fier, may easily be committed· by less tal ented designers to produce an amplifier whose performance bears no more rela tionship to that of the Williamson than cattle to cantaloupes. Electronics, like mathematics, is a language-a means of ex pressing ideas-rather than a science. Us ing resistors, inductors, capacitors, and other characters of the electronic alphabet, it is possible to fashion components and phrases of circuitry that possess clarity, elegance. wit, economy, subtlety, or-in lesser hands-the banality, crudeness, stu pidity, bluntness, and waste of greeting card poetry or prose. Samuel Miller, 122 E. 78th St., New York 21, N. Y. Records Sir: I am about to confess to something ap proaching complete baffiement. I am trying to find out how to equalize a pickup, and can't get to first base. Or rather, I get to six different first bases. Comparing the various articles on the subject in the AUDIO ANTHOLOGY, I can find no agreement on what we are trying to equalize. What are the modern, commonly met re cording characteristics? Surely it cannot be true, as some say, that the recording char NEWCOMB acteristic of any given record depends upon the ;whim-of-the-moment of some ob scure recording technician. One embittered friend suggests that modern recording con soles are equipped with two roulette wheels, mounted on multi position free-acting switch shafts-one marked TRNVR FREQ and the other PRMHSS, IF ANY. Are things as bad as this? Please understand that I would know how to qesign a suitable network if I only knew what I .was trying to design. Per haps you know if any records are available from the larger manufacturers which are cut on their "usual" equipment, with a sine wave voltage of constant magnitude ap plied to the input of the recording console as the frequency is swept over the audio spectrum. (Yes, they are. ED.) Such rec ords might take this whole matter of equalization out of the realm of crystal gazing. entrail-divination, and rune casting. I will very much appreciate any advice and comfort you can offer me. At least, perhaps you will say that everyone is as confused ·as I am. Eugene Altman, 63-61 99th St., Forest Hills 74, N . Y. (We so say. Our advice always is to pro vide adequate fle.~ibility of controls, alld then so adjust them that the resulting sound outpta pleases the ear. ED.)
10 AUDIO ENGINEERING 0 OCTOBER, 1952 II's Ihe new large-hub New improved tape matches reel improvements!
7·in(h professional reel of Supplied on the new]/I professional reel is a new type USCOTCH" Magneli( Tape! of magnetic tape that offers many technical advantages: • New "Dry Lubricating" process eliminates tape and head squeal, produces a tape that turns in a faultless performance under conditions of extreme CUTS TIMING ERRORS! New larger hub reduces heat and humidity. tension changes, cuts timing errors 50% . • New thinner construction allows more than 1200 feet of ta pe to be wound on the new 7/1 reel despite REDUCES PITCH CHANGES! Lower htib-to-out- larger hub. Ma gnetic properties of this new tape are identical in every respect to the older "Scotch" side~diameter ratio means a marked reduction in Brand #111-A tape, the industry's standard of pitch changes bet~een spliced portions of broad quality. casts. • T a pe supplied on the new reel is 100% splice-free.
LESS VIBRATION, FASTER REWIND! Bigger hub • Output variation is guaranteed to be less than plus ~ or minus M db at 1,000 cps within the reel, and less produces 10% faster rewind speed, yet rotational than plus or minus 72 db from reel to reel. speed is lower than that of the standard reel. Oper ation is so smooth that wear on equipment is cut, with resulting maintenance savings.
The t erm "SCOTCH" and t he pla id d esign are regist ered tra de. COTCH BRAND m arks for S o u nd Record i n g T ape m a d e in U. S . A . by S MINNE SOTA MIN I N G & MFG. CO., St. Paul 6, Minn.- also makers of UScotch" Brand P ressure-sensitive Tapes, nUnder seal" Rubberized Coating, "Scotchlite" Reflective Sheeting, AGNETIC TAPE • "Safety-Walk" N on-slip Surfacing, "3M" Aora- Your supplier has the new "Scotch" Brand ~ sives, "3M '? Adhesives. General Export: 122 E. . '1 42nd St., New York 17, N.Y. In Canada: L ond on , 7/1 professional reel with the new Dry o .;;.V On ~. , Can. Lubricated tape. See him today!
AUDIO ENGINEERING • OCTOBER, 1952 11 The British National Radio Exhibition LEONARD CARDUNER '"
An eye-witness account of an annual event at which most of us would be present if it were not so far away, written with the American viewpoint.
ONDON, SEPT. 1, 1952 : A few years ago, Except for the Audio Fairs, however, there when I last visited the British Na are few trade exhibitions designed to at Ltional Radio Exhibition then being tract the man on the street, and most of held in Olympia, London, the British radio those that do exist are held as private industry was just getting back on its feet showings by individual manufacturers or after the war. At that time there .was little retailers. Our trade shows, of course, are activity in television and the 78-r.p.m. rec rigidly closed to the public. ord player was still standard even though The Radio Show in London, however, is 33 1/3 r.p.m. had already become an iin not merely an exhibition of equipment, it pressive trend in the American phono is a place ,where people are invited behind graph industry. This year, however, the the scenes of radio and television, meet Exhibition indicated the wide-awake, up quite a few of the entertainment people to-date attitude which has been reflected they normally see or hear from afar, and by the success of certain British electronic talk directly with those who design and and audio products in our own country. manufacture the sets. Quoting from a re For example, British three-speed record cent description of the show, "It is the rec players are now virtually standard in Eng ognized annual get-together of the listening land, and indeed such machines as the Gar and vie.wing public, the B.B.C., and the rard (well known to American enthusi manufacturers and dealers, and a celebra asts) are seen not only in high-fidelity ar tion of the opening of another Autumn and rangements but are furnished with the ra Winter season of good listening and view dio-gramaphone combinations of the major ing." No amount of advertising and mer I'adio manufacturers. chandising ingenuity can describe the s01md No longer at Olympia, the National Ra of high fidelity reproduction; no illustra dio Exhibition was held fo r the second year tion or description of the clarity of televi at much larger quarters, in Earl's Court, sion pictures can do as much to sell televi l:ondon. This additional room made pos sion as an actual demonstration. During SIbl e various elaborate demonstrations the past few days, I have seen almost ev aimed at giving the visitor a sense of al ery British radio receiver of any impor most personal participation in the processes tanc~, as well as broadcasting and commu of radio manwacturing, television broad nication equipment, short wave, short range casting, and military communications. communication for professional and busi England's radio show is one of the three ness purposes, navigating aids, industrial most popular public exhibitions in Great and medical electronic equipment and com Britain. It is the largest radio show of any ponents and tubes. held in the world, and in fact, has no coun- I do not remember any radio show, trade . terpart in the United States. Every effort or otherwise, where there was so much to seems to have been made to keep the exhib interest the technical man as there is here its fresh, lively, and topical--entertaining in Earl's Court this year. The Radio In as well as informative. For example one dustry Council's control room suite for ex fascinating exhibit, of the type bne ;lever ample, is the nerve center of all the televi sees in American shows, was by the manu sion and radio demonstrations at the radio facturers of Multicore Solders. A television show. Through this control room pass all camera was actually being assembled with the signals for the television programs seen some 10,000 soldered joints being made on throughout the show, as well as the sound each equipment. These Pye television cam programs and announcements heard on the eras. after the Show, will be sent back to loudspeakers. This Control Room suite is their Plant at Cambridge for test. I am in divided il1to three parts, and has glass walls formed that it was the largest practical so. t~lat visitors can see all that happens working demonstration ever seen at the wlthm. radio show. The Announcer's Studio, whim is fitted Walking through the busy floors among with twin turntables, is occupied through the thousands of people, who obviously are out the Show by attractive girl announcers the general public not connected with the who link together the various televisio~ industry, I almost had the same impression and sound items which are heard through I used to get at the great American auto hundreds of television sets in the Exhibi mobile shows before the war, :when ever3' tion. one went to see the new cars whether he An innovation this year is that public was buying or not and whether he made announcements are seen as well as heard, cars, sold them, or merely rode in them. for a television camera is installed in this About a quarter of a million visitors pay Studio. Another section of the suite housed to see the British Radio Show each year. the elaborate television distribution ampli In the United States, we now have the fiers. This enables the output from fiv e dif Audio Fairs to interest the ever increasing ferent sources to be fed through to all the numbers of people who want to li sten to sets in the Exhibition. The sources are the the finest in home musical reproduction. B.B.C. television programs as transmitted daily from the main transmitters, which * British lndl-tstries Corp., 164 Dnane Sf., now cover 80 per cent of the population of New York 7, N . Y. Great Britain; the Announcer's Studio de-
12 AUDIO II'fCINEERINC • OCTOBER, 1952. From the research laboratories of Webster Chicago comes the new HF series Diskchangers -designed and engineered especially for the • Webcor HF has one simple speed challenging task of gently, quietly and quickly control, conveniently located. It changing records in the finest high fidelity is easily acces~ible in all types of installations. installations. Wherever one sees the handsomely designed Webcor HF Diskchanger, it is the symbol of both quality and luxury. No other changer • Webcor HF has an exclusive made delivers the satisfaction that comes with "muting switch" for silencing the the trouble-free operation of the master me amplifier during the record chanical part of any HF installation. changing.
• Webcor HF series has the Webcor Webcor HF is a "push.off" type exclusive electrostatically flocked changer considered by experts to turntable wliich forms the thickest ~ . be the most gentle method of carpet to provide the softest changing records. cushion for record drop.
Webcor HF series has an extra I. ~c.<>-(" I · Webster-ChicagoW.b~, HF ~ .."'.. Vel o The HF series is available in five models: Webeor 127-HF-a bose pan Webeor 127-270-HF - a bose Webcor 126-27-HF-a replace model equipped with turn pan model equipped with a ment Diskchanger for use over crystal cartridge. G.E. Triple Ploy variable re Webeor 127-27-HF-a bose pan luctance cartridge. ~~!~c i~~i~~~~~ielu~~:~c~rl~~ model equippeq for use with ¥lebeor 126·HF-a replacement cartridges. individual plug-in magnetic Diskchanger equipped with or variable reluctance car turnover crystal cartridge. tridges. AUDIO ENGINEERING • OCTOBER, 1952 13 scribed above; a section on the ground floor of the Exhibition ;where celebrities are interviewed; a film scanner in the Radio Industry Council Control Room. which provides film programs when no others are available, and rehearsals of transmissions from the giant B.B.C. Studio, which is situ ated elsewhere in the Exhibition. This Studio, which cost nearly $60,000 is the largest in Europe, has been specially INTER MODULATION METER built for the ten-day run of the Exhibition Professional Flexibility and Precision and has a thousand free seats. Items for the at Reasonable Cost B.B.C. Television programs are rehearsed in this Studio during the day under the Model 165 1M Meter is especially suited eyes of visitors, and then transmitted in the for laboratories, broadcasters, recording evening through the B.B.C. national net studios. Combines signal sources, analyzer, work. Naturally, arrangements have been voltmeter in single compact case. Reads am· made that the rehearsals can be seen on plifier output voltage, %IM directly on the television sets in the Exhibition. meter. Provides for use of oscilloscope to The layout of the Exhibition is divid~d determine causes of 1M; full graphic instructions supplied. Wide range of test frequencies; roughly into four sections, namely the mam 60 cps internal, 40-200 GpS external for LF; standard 2, 7, 12 kc internal, 2·20 kc external booths in the center of the hall, which are for HF. Selectable voltage ratio of 4 : 1 for LF testing and 1 : 1 for more accurate HF most elaborately decorated, the approxi testing. Less than 0.1 % residual 1M thru use of accurate bridg e -~ype mixing circuits and mate cost of most of them being in the re toroidal-core filters. 8%:' x 19" rack-type panel; 8%" deep. Price $250.00. gion of $12,000. Most of these booths would Model 165D provides for 40-400 cps external LF signal, for di sc reproducer and hearing aid have at least a dozen television sets in measurements. Price $350.00. operation. Many of the manufacturers oc cupying these booths also have elaborate More Accurate Readings with NEW BRIDGER sound-proof demonstration rooms and suites Only 3 mmf Input Capacity of Sales Offices. One ,whole wing of the In bridging measuring instruments across high-Z circuits, Exllibition is occupied by separate e. .-"hibi minimum possible loading is vital. New Model 100B Bridger tions of the Navy, Army and Air Force, in with improved cathode follower and special double-shielded cluding the first display of a radio-guided cable has negligible effect. Input Z at tip of 3 ft. cable: now missile, and two 'demonstrations of under 70 megohms shunted by only 3 mmf. Output Z: 200 ohms. water television including one in which Output/ input voltage ratio: 0.99. Usable to several hundred divers are seen descending and ascending kc. Price $96.50. to and from a wreck. Other electronic 110V elties include radio controlled model ships in a giant tank; an electronic "Doorman" who greeted foreign visitors in anyone of 16 languages and gave particulars of what was on in the show each day, and a prac tical demonstration of how the British Gen eral Post Office, .with a mobile truck, detect British viewers who have not paid their I icense fees. For reverberation tests, experimental phonet- The trend of development in England is ULTRA-SPEED RECORDING ics, propag'ation studies, any fast-changing affected to a considerable extent by the purchase tax which is 66 2/ 3 per cent of with the LOGGER widely·varying phenomena. Logger feeds di- the wholesale price of all radio, phono rect-writing oscillograph providing convenient low-cost inked record. Chart scale is linear graph. and dommestic electrical equipment in db, with pen speed adjustable up to 10 to 20 times faster than usual high speed level other than amplifiers. Nevertheless there recorders. Also available without oscillograph. was shown an extremely wide range of Logger shown consists of new stabilized converter, linear rectifier, VTVM, oscillograph television receivers. One characteristic of driving DC amplifier. System is insensitive to temperature variation ; is inherently log the British range of sets is the number of arithmic and independent of tube characteristics. No motors, clutches, thermostats. Models projection models which were on show at 121, 122, 124 with 50 db range; 121W. 122W, 124W ,vith 60 db range. Available for DC Earl's Court. This included one television and RF, and with other db ranges. set giving a picture 4 x 3-ft. and the whole MINIATURE PREAMPLIFIERS for apparatus being housed in one cabinet, the KeIJogg Condenser Microphones (below) picture being transmitt.ed from .t~e re~r. There were several eqUlpments glvmg PIC Also available for 640AA. tures of similar size involving front pro Stability, linearity, and low noise level of best condenser microphones are available at jection. moderate cost with these units. Models 12, 14, 16: for AC or battery operation; available with insert resistor for convenient calibration. For acoustical laboratory or precision record ing, these miniaturized units, only Ph" o.d., offer minimum disturbance of the sound field. Prices from $130.00. Binaural Demonstration KELLOGG MIDGET CONDENSER MICROPHONES. The demonstration of greatest interest to Performance-proved for over 15 years. Feature spring-controlled diaphragm tension with the high-fidelity enthusiasts was one staged lo~g-term calibratio~ stability. Reasonable cost and prompt delivery, calibrated if you by the British General El'ectric Company, WIsh. We are authOrIzed dealers for these excellent microphones and will be glad to advise to demonstrate the high fidelity obtained by you. Phone or write us. their KT66 valves. It was an impressive "Binaural" Sound demonstration. Sitting in a comfortable seat in the large room, I GALV ANOMETER PROTECTOR heard two people play a duet on a single Model 170-Galvo-Protector increases speed and convenience of tambourine. I could hear the tambourine bridge measurement and protects galvanometer from damage being thrown from one side of the room to through overload. Automatic non-linear network with no movin'" the other. A dance band played some of the parts redlllces galvanometer sensitivity when bridge is unbalanced~ latest tunes, and I could clearly detect that but affords maximum sensitivity near point of balance. Price $24.50. the violins were on the right and the drums on the left. A piper marched up and down ,I from one side of the room to the other. It I ; was impossible to determine that the repro duction was undertaken by mechanical ~ d · INSTRUMENT Write now for Catalog A. means. In fact, the whole progr'am had been COMPANY INC recorded by using two input channels on ~ U 10 See us at the Audio Fair. dual-track tape, which was then reproduced Dept. :: 133 WEST 14th STREET , N . Y II, N Y [COIl tinned on page 81] 14 AUDIO ENGINEERING. • OCTOBER, 1952 to the E. E.or PHYSICS GRADUATE with experience in RADAR OR ELECTRONICS Hughes Research and Development Laboratories, , , .- one of the nation's large electronics organizations, is flOW .- .- , creating a number of new openings (-,------, , in an important phase of its operation. " " Here is what one of these positions offers you: 1.THE COMPANY you will work in our Laboratories or overseas (single men only). Hughes Research and Develop for several months until you are Compensation is made for traveling ment Laboratories is located in thoroughly familiar with the and for moving household effects, Southern California. We are pres equipment you will later help the and married men keep their ently engaged in the development Services to understand and families with them at all times. of advanced radar devices, electron properly employ. ic computers and guided missiles. 5. YOU R FUTURE 4. WHERE , YOU WORK 2.THE NEW OPENINGS You will gain all-around experience After your period of training (at that will increase your value-to The positions are for men who will full pay), you may (1) remain with the company as it further expands, serve as technical advi~ors to the the company Laboratories in in the field of electronics. The companies and government agencies Southern California in an instruc next few years are certain to see a purchasing Hughes equipment. tion or administrative capacity, large-scale commercial employment Your specific job would be to help (2) become the Hughes representa of electronic systems - and your insure the successful operation tive at a company where our training in the most advanced of our equipment in the field. equipment is being installed, or electronic techniques no~ will 3.THE TRAINING (3) be the Hughes representative qualify you for even more Upon joining our organization, at a military base in this country- important positions then. HOW TO APPLY If you are under thirty-five years of age, and if you have an E. E. or Physics degree, with some experience , , , in radar or electronics, , , ------~, write to: HUGHES RESEARCH AND DEVELOPMENT LABORATORIES Assurance is required Engineering Personnel Department that relocation of the applicant will not cause CULVER CITY, LOS ANGELES COUN jf Y, CALIFORNIA disruption of an urgent military project. AUDIO ENGINEERING • OCTOBER, 1952 15 Field recording till now has posed a real problem for the en· Take the CUB CORDER anywhere ... to the local airport to inter gineer. He has either been saddled with cumbersome e quipment view a V. I. P .... to a disaster scene to interview witnesses that required power lines involving hours of installation time . .. to the stadium to record the color of a football game. Wher or has been provided with a so·called "portable" tape machine, ever you take it, the CUB CORDER is ready for instant use. either spring or battery driven, with wide speed variation, con· The CUB CORDER is an indispensable piece of equipment for siderable distortion and short life power supply. ev~ry broadcast station, newspaper, recording company and But, the new CUB CORDER brings a new era to field recording. school and has a multitude of uses in almost every industry'. With its light weight (only 12% pounds), compact size (smaller than a portable typewriter case), exceptional speed accuracy and rugged dependability, i~ becomes the most useful of all Write today for the new booklet describing the CUB CORDER po~table tape machines. . .. America's'handiest, most useful, truly· portable tape recorder. What other portable ,rec;order has these features? • Self-contoined power supply from rechargeable • Frequency response to 6,000 cps. wet batteries. • light in weiglit-12% pounds. • Batteries easily charged. from auiamobile ciga. rette lighter outlet. • Smartly styled, leather-grained case with • Precision, constant speed motor. shoulder strap. • Two standard tape speeds. • Instant operation-easy maintenance. ~ CS lr III @)" II INI·, CS 0 DELAWARE 1, OHIO FORMERLY CIRO CAMERAS, INCORPORATED 16 AUDIO ENGINEERING • OCTOBER, 1952 Television Ehgineerriti, by Donald G. F ink. N e.w York : McGraw-Hill Book Co., Inc., 1952. x iv +720 pp., $8.50. Although this book is presented as the second edition of the well-known classic :'Principles of Television Engineering," it IS practically an entirely new volume. Over 90 per cent of the text is new, as is some Coming Up 85 per cent of the illustrations. The only resemblailce the present book bears to the original is the excellence of the presenta tion, the coherence of its contents, and the clarity of the exposition. . Pe:r:fect The text covers the basic principles of television systems, the analysis and synthe sis of television images, cameras and pic ture tubes, scanning and synchronization methods, the transmission and reception of Precision television signals, and an exceptionally ex cellent presentation of color fundamentals for television engineers and a description and analysis of the various color television systems that have been proposed. .Prints Each chapter of the book is suppl emented by a very complete and lengthy bibliog raphy covering both other books and the contemporary literature. In addition, a se ries of exercises are appended to each chapter. Finally, an author and a subj ect index both extensive, are included. Here your film receives its T elevision has grown to the extent that it is no longer possible to present within first, careful inspection. Ex the confines of one volume a complete dis perienced workers examine it sertation covering all facets of the science. for defects, check over splices, Thi s book, howeVer, presents in the clear perforations, synchronism of style that is characteristic of all the au sound track general condi thor's writings the fundamentals of both tion. Your printing instruc monochrome and color television. It is a tions are carefully correlated book that should ·be in the library of ever y engineer and' student concerned with tele to the film itself. vision. -H, A . Ch inu Television Explained, by \""1. E. Miller. YOUR ASSURANCE OF London, England: Iliffe & Sons, 1951. 104 + xxiv pages. 5 shillings. BETTER 16mm PRINTS Television Principles, by Robert B. Dome. New York: McGraw-Hill Book Co., 15 Years Research and Spe. enable us to offer service un· Inc., 1951. 291 + x ii pages. $5.50. cialization in every phase of equalled anywhere! T ogether, these two books present a most 16mm processing, visual and interesting coverage of the television tech aural. So organized and equip Newest Facilities in the 16mm nique as it exists today. As its title would ped that all Precision jobs are field are available to customers rightfully suggest, Television Explained of the highest quality. of Precision, including the most is the simple story of what happens in a modern applic ations of elec· television receiver, and it is as applicable Individual Attention is given tronics, chemistry, physics, optics, to us in America as it is in its native habi each film, each reel, each scene, sensitometry and densitometry tat, with the exception of the change in line and frame frequency, and of course each frame - through every incJuding exclusive Maurer· the reference to the BBC test card, which phase of the complex business of desi"gned equipment-your guar· is carefully analyzed to show the h ults it processing - assuring you' of the antee that only the best is yours will expose in a receiver not correctly ad very best results. at Precision! justed. On the other side of the picture, M r. Our Advanced Methods and Dome enters deeply into the higher math our constant checking and adop. ematics of design of circuit parameters tion of up.to.the.minute tech. and the needs imposed on Hlem by the wide niques, plus new engineering pass band they must accept. This is a book fo r tRe man who is as facile with mathe principles and special machinery matics as with eating, and should not be attempted by one seeking rudimentary data. But in its scope it is well worthy of a posi tion on the engineering bookshelf of the de Precision Film Laboratories - a di signer of TV sets both for today and for vision of J. A. Maurer, Inc., has .l4 some while in the future. years of specialization in the 16mm Chapter endings contain review questions field, consistently me.ets the latest de and answers, and there is a generous in mandsfor higher quality and speed. clusion of tables of reference data, curves and charts. These clarify the points of the text which cover the history of the art right up to the state of development, at the time of printing. -LBK AUDIO ENGINEl'RING • OCTOBER, 1952 17 EDITOR'S REPORT / T HE AUDIO FAIR the phonograph. Like most inventions of a complicated nature, the phonograph has come' a long way in its three OMES OCTOBER, and along with the falling leaves quarters of a century. The modern home sound installa comes The Audio Fair-each year bigger and better tion bears but little resemblance to the earliest sound Cthan it was before. Bigger this year in that it lasts reproduction apparatus-either physically or in the qual for four days instead of the three in the past years; and ity of its sound output. Originally conceived as a business better in that there are more exhibitors with more prod machine, the phonograph plied that market for many ucts to show. There is no question that the public is years befo re it made its way into the living room. And becoming more quality-conscious with respect to its while it is now firmly established in the living room musical reproduction-as well it might after many years also nursery, soda parlor, tavern, and even the broad of accepting what is offered by the set manufacturers. casting station-it is still a force in the business world. Some of this we may attribute to TV, for while the Many of us in audio for entertainment applications are newest art is certainly popular, there are still many who completely unfamiliar with the advances in related fields. are not amused by combined sight-and-sound entertain Audio is not limited in scope. Audio techniques ' are ment. Notice, for example, how many more hours of employed in many fields . Much of the glamour is related valuable evening listening time have been devoted to to music and broadcasting and other aspects of enter concerts of both light and classical music on the radio tainment, but we must not lose sight of telephones, busi networks. ness machines, medical applications, military uses, hear Thus with more good music on the air. there is more ing aids, acoustics, and the other fields in which audio reason than ever before to investigate the new items in is important. the audio world-and plenty of opportunity during the All of us like recognition for Our work, particularly four days of the Fourth Audio Fair-October 29, 30, when it is completely unfamiliar to most people. And on 31 , and November 1. The Place ?-Hotel New Yorker, behalf of the recording technicians who turn out the con in New York City. Details of exhibit hours wi ll be found stantly improving platters, we thank N ewsweel? for con on page 83. sidering that branch of our industry worth the space Along with the Audio Fair wi ll be held the Fourth required to present this feature story. Annual Convention of the Audio Engineering Society same place, same days. An impressive program of tech HOME CONSTRUCTION nical papers has been arranged, and for a li st of these papers, turn to page 58. '!'( e had never before particularly regretted our in abilIty to read J apanese since there is still much in more REG IONAL AUDIO SHOWS ~ami lia~ languages whi~h we have yet to read. Not, that IS, until we received the current issue of The Rad-io While the Audio Fair-as above-will undoubtedly emft M onthl'jl, which shows in detail how to construct remain the principal focus of interest from the stand a capaci~ance-type phonograph pickup. Whether we point of exJlibits, not everyone is privileged to attend could build .one or not from the pictures alone is not for any number of reasons. But this does not lessen the know~, but .It seemed like an interesting project. desir~ to visit a showing of audio equipment-and to Thl~ partlc.ular magazine devotes a lot of space to con hear It-regardless of the fact that the trip to New York struction art1cles-reminiscent of the radio magazines may n?t ~e feasible. The solution-as already put into in this country in the 20's and early 30's. One }E reader operatIOn 111 a nWl1ber of centers-is the regional show. from :'down under" gave us to understand recently that One very s ucc~ssfu l one was held recently in Memphis exper ~111ent ers and hobbyists in his country wouldn't buv under the auspices of a local distributor and another is ~nythll1g tllat .they could build-as a matter of pride, so being held in Philadelphia under the cO;11b ined banners It seems. Havl11g gone throlwh those stages many times of three distributors. we know just how he feels. As a matter of fact we al~ This event- the Second Annual High Fidelity Con ways have more things planned for the future than we ference and Audio Show-will be held in the Crystal ever expect to get around to building, but it is refre ~h Rooms of the Broadwood Hotel in the City of Brotherly ll1g to plan-at least, life is never clulr: Love on October 8 and 9. The first annual etc. etc. held . Somebody of course, hand-built the first phonograph last year was completely successful, and points the way pickup, . the first transformer, the first loudspeaker. to more such regional shows throughout the country. May l~e 1t would be int~re ?t ing to go back to those days We salute those ""ith sufncient faith in the future of occaSIOnall y, although It IS probalille that the manufac audio to make the effort to acquaint the public with tured product is far superior to those we miO'ht turn out what the industry offers. Every step in this direction is in the home workshop. But let us not lose "'siO'ht of the a step forward. fact that the entire hi-fi industry stems from the desire of many early experimenters to have something better MEN BEHIND MIKES than was available commercially. The manufacturers have pretty ~ve l! caught .up with the experimenter-if We note a recent issue of Newsweel? (September 8) not passed 111111 111 most 1l11es. But there's still plenty of in which the work of the men responsible for modern room for both the man who builds his equipment and the phonograph records is finally recognized, the occasion man who buys it ready made-and both will continue to being the 75th anniversary of the first announcement of get pleasu~e out of ilie final result. 18 AUDIO ENGINEERING • OCTOBER, 1952 Pickering High Fidelity Components are available ihrough leading jobbers and distributors everywhere; detailed literature sent upon requell. Address Deparlment .If AUDIO ENGINEERING • OCTOBER, 1952 19 M UCH of your Long Distan ce tele phone system works thr ough cable hut open Same .wires- wire lines are still the most economical in m an y places. Thonsands of these circuits • are so short that little would b e sa ved b y using el aborate carrier telephone systems which ar e better suited for lon g-haul many more vOices routes_ But a n ew carrier system ___ the T ype 0 design ed especially for short hauls ... is changing the pictm·e. It is Connecting new mnlti-voice system to open-wire economical on lines as short as 15 miles. lines, near Albany, Georgia_ With new system, 150,000 miles of short open-w ire telephone lines W ith T ype 0 thousands of lines will can b e m ade to carry up to 16 simultaneous carry as many as 16 conver sations apiece. m essages economically_ T ype 0 is a happy combination of many elem ents, some new, some u sed in new ways_ As a result, terminal equip m ent t akes up one-eigh th as much space as before. Little ser vice work i required on location ; entire apparatus units can b e removed and replaced as easily as vacuum tubes. Moreover, the n ew carrier system saves copper by multiplying the usefulness of existin g lines. For telephone user s i t means :plore ser vice ... while the cost stays low. Repenter equipment is mounter! at bn,e of pole in cabin et at right. in ensy-to-service position. Left ha nd ca.bin et houses emergency power supply. System enlploys twin-channel techniq ue. tra nsmi tting two ch a nnels On a sing- Ie cnrrier by using upper a nd lower sideba nds. A single o$ci lJ ator serves two channels. BELL TEL E' P H 0 N E L A B,Q R AT 0 R I E S '\-.. Improving tele p, pone service for America\ provides careers for creative men in scieptific and te,chnical fields Intermodulation, Distortion RICHARD C. HITCHCOCK':: A brief and frank discussion of this form of distortio n, and the description of some simple devices which will enable the experimenter to make his own measurements with a minimum of equipment expense. -E WAY TO TEST an audio ampli fi er is to play records at full volume, 1.0 o Oa nd li sten for "muddy" or "harsh" tones in the upper register. These hap pen when a hi gh-frequency tone is 7 affected by a low-frequency tone_ • .1 0 ;!; 100 ~1000 Testing the amplifie r by listening IS " LOW" !:i I- / the fi nal authority, of course_ But it Fig. 3_ Transmission g L OW PASS t:l I woul d be desirable if tests could be made curves for high· and q to fin d out how much distortion the am low-pass filters used ~ 0,I X HIGH PASS plifier introduces. Even the best amplifi er in th e autho r' s .... measurements. "o has some distortion. The only questions VI \ !:i are, how much, and what kind ? o > 1\ As a start, let's consider three notes 30 on an 88-note piano. The hi ghest note, • \ N o. 88.. is C. Note No. 87, next lower" is B . It you should strike these adjacent .0 , IJ ~ notes at the same time, you probably 100 ' ,000 10,000 FREOUENCY - CYC LES PER SECOND Most music on records incl udes more r.p.m.) is available, using 10017,000 than one tone at a time. The interacting cycl es per second 4: 1 ratio. It might be of these tones cause more or less inter mentioned, in passing, that a record modulation distortion. F or measurement, introduces another variable in an already it is much simpler to consider only two complicated situation, and that the test pure tones, one hi gh and one low. W ork of the amplifier alone is the best step to ing with these will give us some idea of take first Further, a test record wears, amplifi er distorti on. whereas an oscillator will work for a Incidentally, there is no accepted much longer ti me_ standal-d of a "high" or of a "low" tone. OSCILLOSCOPE One company publishes data3 on its Preli minary Procedure ampli fi er tested at 6017,000 and 40/ 12,- W ith the equipment of F1:g_ 1, playa 000 cycles per second, with a low-to Fig . 1. Bos ic circuitry used in preliminary set-up. hi gh-frequency sine wave and notice that high-note ratio of 4: 1. Another" shows the amplifier output is a good sine wave, 40/ 2,000 ; 4017,000 ; and 40/ 12,000 a ll too. Set the timing- rate of the 'scope so with 4 :1 ratios. An excellent a-rticle' woul d call the result 'a ".discord. " You that it gives a full wave (or more) of would hardly think an amplifier was very the low tone, and with the high tone still good if, when call e.d on to reproduce the playing, add the low-frequency tone. The note C of the piano, it also gave the pi cture on the 'scope will be pretty, but adjacent B, a few hundred cps lower. difficult to analyze_ So next we open the Yet this is what a poor amplifier does circuit at XX and insel-t a high-pass do- and here we arrive at an important : ~<>---11-----+-( -----+-~=K : : I filter, F'ig. 2. T hi s will allow only the fact. The amplifier adds the extra note, high frequency to pass to the oscill o the B, only when a certa in low-frequency scope, in accordat)ce with the transmis tone A is played at the same time. Fig . 2. High- pass filter configurat ion. sion of the fi lter, shown in Fig. 3, and To go over this again, a poor ampli we can see what happens to the high note fier , called on to reproduce Numbers 38 when the low note (blocked by the fi lter) and 88 on a piano, g ives 38 ( A # ), h om which many valuable ideas were is vari ed in volume_ If you are doing this 88 ( C), plus the ex tra and unwanted taken for the tests indicated here, for the first time, you will be astounded notes 87 (B) , and an even higher one recommends 40/ 4,000 cycles with 4 :1 to see how ragged the formerly smooth which we may call No_ 89 (C#) a half low-to-high I-ati o. A recent paperu sug high note becomes. tone hi gher than is on the piano. The gests 60/ 4,000 with any of three ratios ; T hrough the hi gh-pass filter will go reason for this is the low-frequency note, 4 :1;· 1 :1 ; or 1 :4. A test record' (33 the notes 87, 88, and 89 of our example No. 38 on the piano, the note2 A #. This but No. 38, the one which causes these is one kind of intermodul ation distortion. 3 T ransfo rmers in W illiamson H igh Fidelity Amplifi er, Form 382, Standard extra 87 and 89 notes, will not get T ransform er Corp. through _ W e can now see the effect of ':' Enid Pla.netarill m, Pi t tsbll~' gh 12, Pa. 4 Ultra-Linear Williamson Amplifier, the low tone on the high one, but sti ll I For A = 440, the vibrations per second Acro Products Co. we want to measure this effect, this dis for Num bers 88 and 87 are 41 43 and 3910 5 T homas Roddam, "Intermodulation tortion. respective ly. Their difference is 233 vibra di stortion," Wi'reless World, April 1950_ N ovv add a rectifier and low-pass tions per second _ 6 Piel-ce J. Aubry, "Intermodulation fi lter, F ig_ 4_ T he recti fi er cuts off half testing," AUDIO E N GI N EERING, Dec. 1951. 2 For International Pitch, A# is 238 vib the waves and the low-pass fi lter takes rati ons per second. 7 Cook Series 10 Test Recore!. AUDIO ENGINEERING • OCTOBER, 1952 21 out the hi gh-freq uency tones. At ZZ, the Equipme nt Requ ired end of the low-pass filt er, is the dis F irst, then, we need a two-tone sine tort:on we want to measure. Fig~we 5 wave generatOl· 8 • 9 having frequencies of shows the complete arrangement, to be 100 and 5,000 cps. E ach must have its inserted at XX of Fig. 1, ahead of the oscilloscope and voltmeter. For compact own volume control, so that any amount LITt r\ of each frequency can be supplied for reference, we shall call the voltage across Fig. 4. Rect if ie r and low-pass fi lter circuit. X X (nearest the amplifi er of F igs. 1 test. F ig llre 6 shows a suitable instru and 5) I N; across YY, HI; and across ment. ZZ (next to the voltmeter and 'scope Second, we need a voltmeter which is Fig. 5), LO . T he di stortion is the ratio good at audio frequencies, to read I N, IN21 B LoI HI, or in percentage, 100 x Lolrn. HI, and LO. If the amplifi er to be tested TO 30 AMPLIFIER mh The equipment has been chosen to be has less than 1 per cent distortion you x o---+-~--~~--~----~h useful for tests other than distortion. will want to measure as low as .01 volts For instance, the high note has been full scale. This means that your voltmeter chosen, not at the 4143-cps pi ano C, but must include an audio amplifier. F·ignre IN at 5,000 cps, because this is a good place 7 shows a suitable vacuum-tube volt , to test an amplifier fo r treble boost. F or Illeter with ranges 100/ 101110. 11.01 volts SELECTOR VOLTMETER J ACK a similar reason, the low frequency is full scale. Maximum stability is obtained 100 cps ; this also tests one of the low by using 20 db feedback (10:1 in volt Fig. 5. Assembled circuit including high-pass frequencies an amplifi er should do well , age) for all but the .Ol -volt range. The filter, rect ifier, low-pass fi lter, and suitable and can be used to indicate bass boost, switch marked "xl and x lO" cuts the sw itching . t.oo. feedback out or ' in. U sing feedback (xlO ) the sensitivity is 50,000 ohms per .001 volt and the ranges are-100/ 10/ 1I0.l volt 5,000 20 full scale. W ith the "no feedback" (x 1 ) + ~ setting, the meter has 500,000 ohms per volt, with ranges 10/ 1/ 0. 110.01 volts full scale. T he actual nieter is a 100 mic ro ampere a-c meter whi ch has an internal OUTPUT rectifier. A 100-lota d.c. meter could be used with an ex tem al bridge of four IN 34 germanium diodes. In any case, the instrument must be calibt'ated after com pleting the construction work. ~ ~ ~ ~ ~ T he third requirement is the filter ~ on + + + Intermodulation Distort ion T ests 20 20 20 Connect a resistor R , on the audio amplifier output, to "soak up" the audio energy; a resistor with the same ohmic value as the impedance of the speaker Fig. 6. Suggested circuit fo r two-ton e 1M signal generator, you intend using with the amplifie r. T he wattage rating of the resistor should be O F F ~ g reater than the amplifi er's rated output. You can use a monitor speaker at re duced volume, by employing a 100-ohm I tO V 1(1 resistor in series with the speaker across . 01 0 .1 the resistor load, as in Fig . 1. INPUT IV 6SJ7 6J5 I Most of the energy will be in the low f f f frequency tone; turn up the 100-cps ~ O.IV on I on OJ <3 ci tone from the two-tone generator until ci ci ~ the voltmeter across R , ( I N ) shows the .OIY voltage fOt- rated ampli fi er output. Ex ~ 1.0MI ; ~ ample: for a lO-watt amplifier, con §. 0 on ..; SEE nected for an 8-ohm output, = + 8 TEXT P Ei / R; 100 §. 0 .1 "'. therefore E2=P x R = 10 x 8=80; E = . to " V 80 = 8.95, approximately 9 volts. Use range 10 on voltmeter (xl) or range 1.0 ., (xlO ). This 9 volts should produce a FEEDBACK SWITCH 25,000 to,OOO clear sound in the monitor, or' a smooth wave on the 'scope. If the wave is di s torted, reduce the voltage sufficiently to FULL-SCALE RA NG ES + + get a clear sine wave, either audible or ~~fir~~ FEEDBACK SWITCH 20 20 = SETTING )1. 10 Jt 1 visual. Suppose you can get 8 volts 10 100 10 [Coll tinued on page 56] 10 0.1 0 .1 .01 0 .1 .Ot 8 Ginztoni and H oll ingsworth, "Phase shift oscillator," Proc. I.R.E., F eb. 1941. Fig. 7: Sim ple a.c. vacuum-tube voltmeter useful for many other measurements in addition t o 9 McIlvaine, Rectifier T ube, U . S. P at. 1M testing. 1,946,354, Feb. 6, 1934. 22 AUDIO ENGINEERING • OCTOBER , 1952 / A Critical Feedback Analysis HAROLD KLIMPEL ':' The author presents a simple and easily understandable concept of the effect of feedback on input and output impedances of tubes around which a feedback path is provided. NE OF THE EARLIEST applications of The points wherein this analysis differs Introducing Feedback positive feedback occurred when from that published in some papers of To make the amplifier of Fig. 1 degen Oregenerative detectors. made possi the past are as follows: ble the reception of weak signals with erative, the load resistor is divided into 1. The mathematical sign of ~ is neve r two parts. R o and R c, the grid return only one- or hvo-tube sets. Even today, negative. some receivers still use regenerative in being made to the junction of these two 2. Feedback affects only the input, not . resistors, thereby making the voltage E e, termediate frequency stages to obtain the output impedance. g reater pulling power. common to both grid and plate circuits. 3. Feedback, either negative or positive, The amount of feedback in this stage The use of negative feedback began does not affect the plate resistance of in the earliest days of the vacuum tube any tubes in a feedback loop. will be governed by the amplitude of the when neutral ization was employed to feedback voltage Ee which, in turn, is To review briefly an amplifier with determined by the ratio R e/R! also stabilize ]'adio freq'uency amplifiers in out feedback, Fig. 1 is a circuit of a 6Js both receivers and transmitters. The de known as ~, since ~ itself can be defined triode which has a plate resistance of as the percentage of the total output velopment of multigrid tubes eliminates 7,700 ohms and a mu of 20. The gain of the necessity of neutralization, although voltage that is fed back for feedback any stage is expressed by the familiar purposes. Mathematically this is a ll triode transmitter stages today still A= I-I-R L (1) Rp+R! q. q. where ~t = amplification factor of the. , I I I flo tube I I Eo, Rp = plate resistance of the tube I I I L_ B+ R! = plate circuit load I R! Ep If the plate load for the 6Js is made I r - I I equal to the plate resistance, the gain I I ,I Ec, from Eq. (1) will be , I L-______-+ __ ~--~~ + V V A=-20(7,700) (2) B+ 7,700 + 7,7DO -154,000 Fig. 1. Basic amplifier circuit without feedback. Fig . 2. Rearrangement of circuit elements to 15,400 provide feedback and to clarify operation of = -10.0, equivalent to 20.0 incorporate one of several methods of circuit. decibels. neutralization-circuits in which vary R e Eo Ee ing magnitudes of out-of-phase. pl~te In any plate-loaded amplifier calcula K= -=-= (5) voltages are coupled back to gnd cIr tions, the phase turnover must be ac R! Ell AEu cuits to obtain cancellation of grid-plate counted for; the amplifier gain A must from which the resistors Ro and Re are interaction. The entire field of elec appear in all work with a negative sign computed as tronics today demands greater stage sta since the output is 180 deg. out of phase bility, wider band response, and lo\,,:er with the input. For all audio and d . R o=KR! (6) noise and distortion levels. Along WIth applications where the electron transit and other precautions, all of these require time does not enter into calculations, R o=Rt - R e (7) ments can be approximated ,by the judi the mu may be written as 1-1- / 180 °. In The values of i3 can be chosen between cious application of negative feedback. Eq. (2), the mu is understood to be the limits of unity and zero since it is A sizeable amount of literature has 20/ 180°, or simply -20 + JO. A plate always an expression of percentage. In appeared during the last few years on current change through R! ~vil1 produce view of this fact, the sign of ~ is never the impedance changes that take place an output voltage negative since none of the quanti~i es ~n in an amplifier with feedback, notably Eqs. (5)" (6) , or (7) are, negative 111 that associated with the cathode-fol Ep= AEu (3) sign. A degenerative ampilfier has Its lower. A study of this material discloses where Eo = the grid-to-cathode input vol feedback voltage arranged to oppose !he a marked divergence of opinion among tage. input signal, whereas, a regeneratIve several members of the profession on Referring to Fig. 1, the grid circuit amplifier allows the ~eed?ack volta~e .to various principles that underlie the op terminology includes E8 and Ey, denoting assist the signal by bem$' m phase wl~h It. eration of a feedback amplifier, among source and sink voltages respectively. To make an analyS IS of the Ftg. 2 which are the following: Fig~tre 3 shows the 7,700-ohmloadline amplifier, let 1. The manner in which gain reduction that the 6Js of Fig. 1 is working under ; K =0.10, ( 10 per cent of output volt- takes place. a plate supply of 275 volts will drive a age fed back) (8) 2. Impedance changes, if any, of tubes 6.0-ma current through the load and also within a feedback loop. produce a bias of 8.0 volts acro.ss a To assist in comparision, calculations 3. An exact mathematical procedure for 1333-ohm bias resistor. A s.O-volt sIgnal wi th feedback will retain the same determining the improvement attrib 7 700-ohm total plate loael to keep uted to feedback. E8 will produce a s.O-volt drop, Ey, across the input resistance Rn of the tube A=-10.0. The bias resistor from Eq. (6) It is the intent of this paper to outline so the output voltage from Eq. (3) will lI·ill be the effects of energy interchange be be R e = 0.1 0(7,700) tween ampli fi er grid and plate circuits. (9) Ep=-10(5.0) = 770 ohms (4) * 803 Braadac'res, Compton, Cal-if. - - 50,0 volts. from which by Eq. (7) AUDIO ENGINEERING • OCTOBER, 1952 23 R" = 7,700 - 770 = 6,930 ohms. (10) To obtain the proper 8.0-volt bias, a by TYPE 6J5 passed 560-ohm resistol- must be added E . 6.3 VOLTS in series with R e. The pl ate circuit load is still 7,700-oh111s. The p:ate circu·.t voltage gains and losses C2. n be s UI1l111e ~1 up as 12~---+----~--~+-~~--~~--"1-----t----+-----t----i-----t----l Ep=EQ+Ec (lla.) or Eo=Ep - Ee (11& ) The output voltage Eo to ground can be found by substituting in Eq. (11&) for Ep and Ee fr0111 Eqs. (2) and (5) so that E" =AE!J - KAE" (12) = AEy (1 - K) Substituting ci rcuit values from Fig. 2 with a g rid dl-i ve E y equal to 5.0 volts, as in Fig. 1, and a total plate circuit voltage of - 50.0 volts, the output voltage available from plate to ground is E .. =- 10.0(5.0) (1.00- 0.10 ) (13) = - 5u .u 0.90J 45.0 volts. 480 =- PLATE VOLTS Five of the fifty volts generated in the plate circuit exist across the bias resistor Fig. 3. Plate family for 6J5 tube to show effect of feedback on tube performance. R e as a feedback voltage; since the plate circuit is a voltage divider, the output bi as resistor to develop the feedback - 151 .25 voltage Eo is 0_9151 db lower than the . voltage can be obtained by using Eqs. - 5.50 amount generated in this circuit. (12) and (5) in eq uation = 27.5 volts. £.,= Eo - £ o (14) Effect on Input Signal Eo - Effect of I ncreasing Feedback In addition to the plate-circuit loss, = A (1 - E{ ) - KAEo The feedback voltage developed across the feedback voltage Ee also acts to Re wi ll be the difference between the chan~e the voltage equation in the grid and again for Eo total output Ep of - 50.0 volts and Eo CircUit. These grid-circuit voltages can _ Eo KAEo from Eq. (18) equal to - 27.5 volts or be stated as - A (1 - K) - A (i-K) - 22.5" volts. W hen ~ is increased to 0.50, E 8 =E'g - E e (14) B" (1 - AK) the voltages Eo and Ee will be equal in - amplitude, a condition necessary for Substituting in this equation fr0111 Fig. 2, - A (1-K) phase-inverter service. Cathode-fo llower the sig nal E 8 with feedback and rearranging fo.r over-all gain operatiell1 results when ~ is made equal E 8=5.0-(-5.o) (15) E o _ A (1- K) to unity, in which case the entire plate = 10.0 volts. E . - (l- AK) (17) load is R e, since Ro is zero in this case. Notably in television work, the load The grid voltage Ey was assumed to be In this equation, both of the factors impedances often used with cathode 5.0 volts; with a ~ factor of 0.10, there that account fo r the loss of gain in this followers are much lower than plate will be - 5.0 volts of feedback ac ro s~ R e. amplifier are included--(1-K) accounts loaded applications. In these applica F urthermore, only one-half of the input for the plate-circui.t loss and (1-AK) tions, the gain A is reduced considerably, signal E 8 reaches the grid-cathode ter for the g rid-circuit attenuation. This thereby producing smallel- feedback volt minals, the other half bei ng used to ·over change of amplifi cation has not been ages across the load. As long as load come the out-of-phase feedback voltage assigned to a fictitious or appal-ent impedances are fairly high, normal E e. The loss of gain between E8 and E y change of tube mu or plate resistance plate-voltage values can be used since amounts to 6.0206 decibels whi ch added since both these tube parameters have the plate current will be limited by the to the plate circuit loss of 0.9151 db totals been carried through in all calcul ations IR drop in the load. With loads in the 6.9357 db. The gain with feedback IS as stated in tube manuals. nei ghborhood of 75 to 300 ohms, plate equal to By using equations developed in this voltages must be reduced considerably; paper, the Fig. 2 amplifier can be modi- this is confirmed by reference to the 2010g(~ : ) =13 .0642 db . (16) fied to have unity gain by changing the 6J5 curve in Fig. 3. A low value of load ~ value to 0.45, ,in which case the output will cause the load line to approach the The 6.9357 db loss due to feedback voltage using Eq. (13) will be vertical as the load impedance ap- plus the gain above is equal to 19.9999 db, Eo = AEy(l- K) (18)· proaches zero. The operating point must the gain without feedback detenllined in be chosen so the tube will not be driven Eq. (3). Computations in this paper a re =-10.0(5.0 ) (1.00 - 0.45) into either cutoff or saturation regions. = - 50.0 (0.55) 0 carried out to a sufficient number of = _ 27.5 volts. The 6J5 is shown operating with 16 places to indicate the accuracy of the plate volts, which will cause a plate theory; problems in feedback usually The gain A and E ll wi Jl remain U\1- dissipation of 1.28 watts, one-half of its include small differences of potentia l, so changed since the total plate load is rated 2.5 watts. A bias of 4.0 volts places to obtain answers to three or four place still 7,700 ohms. The input signal E s to the operation about midway on the accuracy, six- or. seven-place figures are obtain the above output ' is computed by g raph at this point ; thus the 8-111a often necessary in the work; however, rearranging Eq. (17) so that plotted current will necessitate a load this paper does not imply that seven or E (1 AK) I-esistor of 500 Oh111S to produce the even three place accuracy is necessary to E = 0 - (19) proper bias. Assuming the tube is beirig solve any 01- all feedback pl"Oblems. s A (1 - K) used to feed a properly terminated An accurate equation of over-all stage _ [-27.5(1.00) - (-10.0) (0.45)] 70-ohm tl-an smi ssion line, the tube as a gain in amplifiers using an un bypassed - -100 (1.00 - 0.45) generator will actuall y look into a 24 AUDIO ENGINEERING • OCTOBER, 1952 61.4-ohm load, which is the parall el com = -1.0546 volts. - 5.0 volts of feedback aCT'OSS R I' . The bination of 500 and 70 ohms. The ampli over-all gain: cif 'this stage is fier gain A with this load from Eq. This amounts to an increase of 3.09 (1) will be times that of the 70-ohm load, equivalent to 9.90 db. The 20-db change in line 20 1 0gU~ : ~ ) = 13.9794 db. (28) A = - 20(61.4) (20) impeda:nce is not al\ reflected to the tube 7,70() + 61.4 since it is in paral\el with Re. Actually, This is a difference of 0.9151 db over =- 0.1582 the tube looks into a variation of only Fig. 2, accounting for the (1-K) plate 13.56 db. The amount of feedback under circu i t factor. This tube, even it it were plate-loaded, any feedback conditions is equal to would be an attenuation amplifier since (1- AK), the change in gain that occurs its load is so small that it operates at in the grid circuit. For negative feed less than unity gain. An equation for back, the gain is always negative; posi output voltage can be obtained by re tive feedback, or regeneration, permits a arran~ing .. s.e" eral previously dev.eloped hig her vgltage to reach the g6d than that eguafi6ns for the voltage E e when all the. which is fed in. This same factor, load is ' Illici e up of the bias resistor. (1- AK) , is also the amount by which Using Eq. (5) with substitutions from noise and distortion are attenuated in a Eqs. (7) and (12), we have negative feedback amplifier. Under fhe E =AEg (1 - K)(1 - A K) (21) 700-ohm load, the grid-cathode voltage 8 A(1 - K) E [I wi ll be E . + E e = 2.5000-1.0546 = 1.4454 volts. The feedback will be =Eg (1 - AK) or E y = (1 :_4 K) E . . ( 2.5000) 20 log Ey = 20 log 1.4450 Fig. 5. Rearrangement of Fig. 4 to show intro which substituted in Eq. (5) for Ey duction of feedback in parallel with source. = 20 (0.239) = 4.78 db. K A E s (26) Reduction of Noise and Distortion E e (1- A K) (22) = The amount of feedback at the 70-ohm The remainder of this paper \I·ill be This is an accurate 'statement of the load will 1.28 db, nearly one-fourth that devoted to an explanation of how both voltage developed across an unbypassed with the 700-ohm load. Larger amounts CUTTent and voltage feedback reduce bias res istor in a cathode-foll ower stage of feedback result by using beam pen noi se and di stortion. F'igllTe 6 shows two todes such as the 6AG7 and 6AH6 will when the input E 8 , the gain A, and the ~ feedback paths around the 6J5 tube using factor are all known. Q'ive a o-ain of four. With driving signals E " = 5.0 volts. R 1= 7.700 ohms and Ep = From F ig.' 3, a grid drive of approxi ~f 3.0 ~olt s, the output E e at video line - '50.0 volts. The gl'id circuit equation mately 2.5 volts is indicated since any impedances of 70 ohms will be approxi will be mately 2.4 volts. Between 10 an~ 12 db thing greater will drive the tube into E s+ E [} + Er + E c= O.OO (29) nonlinear operation. A 2.5-volt drive of feedback are the advantages gamed by usino- higher conductance pentodes. will swin g the plate current between 2.5 Identifying K, with the current-feedback and 15 milliampel-es. The output Ee will TI~e use of voltage feedback in an circuit and K . with pl ate-voltage feed be amp Ii fier, diagl'ammed in Fig. .4, is back, the following are true statements : ar.comolished by bddging two reS istors, Eo= [(,E" • ( 30) E = (1.0)(- 0.1582)(2.5) (23) and '0 [1.00:-'( - 0.1582)(l.o)J (31 ) - 0.39550 = Assuming K, = 0.100 and .K, ~ 0.200. the 1.1582 above equation w·ith substltutlOll S are: = - 0.34148 volts. Ec = (0.100 )(-50.0) (.32) This voltage is in series opposition to =-5 .00 volts; the signal E ., so the actual voltage Ey and Er=(0.200)(- 50.0) (33) will be 2.50000 - 0.34148 or 2.15852 = -10.0 va Us. volts. To check the accuracy of the previous equations, the voltage E[I times The input signal E 8 by Eq. (29) with the gain A should produce ~he output = 8+ this substitution will be vo ltage E". Carrying this out to seven E 8 =-( - 5.0)-( -10.0)- ( -5.0) (34) places, the answer is - 0.3414778 volts . . Fig. 4. Method of introducing volt~ge feedback = 20.0 volts. The ability of a cathode-follower to .in series with source of signal. counteract changes in the load it faces Since' there are - 15.0 volts of feedback R!J and Rr across the normal plate load potential opposing E s, the input must can be demonstrated by assuming the R!. There' al'e several other variations previous 70-ohm load changed to 700 possible when using voltage feedback [C oHtinued 011 page 66J ohms which is equal to a 20-db change. using Ry and R r themselves as a I.oad, or The new gain A from E!. (1) the simple expedi~nt shown l1l Fig .. 5. - 20(291.6) In Fig. 4, resistors are proportioned so A 7700 + 291.6 (24) . Rr K = Rr + Ry (27) - 5832 7991.6 A ssuming the total plate load is still A=-0.7297 7.700 ohms, the gain A wiIl also be - 1Q. 0. Assuming Rv and Rr in series at 50,000 where the parallel combination of the ohms R I will have to 'be 111C1'eased to 500-ohm load resistor and the 700-ohm 9.102'ohms so the combination will equal line is equal to 291.6 ohms. 7700 ohms. The ~ factor, K , will then Assuming the. same 2.5-v9It !nput sig- . I;e 0.10 if R y is 45,000 and Rf is 5000. nal. the output by Eq. (22) will be There is no divi sion of the plate-circuit - 0.7297 (1 .00) (2.5) output voltaO'e E " as was the case with E e= [1.00- (-0.7297) (1 .0)] (25) Fig. 2 ; thel~ is no (l-K) f~ctor. Tl~e output Ep will be - 50.0 volts. If the grId Fig. 6. Typical eir-euit involving voltage feed -1.82425 Eu receives 5.0 volts. The 111put must, back in series with source and current feedb.ack = -1-.7='2,-9=-=7:- however, Ire 10.0 volts to overcome the due to unbypassed cathode resistor. AUDIO ENGINEERING • OCTOBER, 1952 25 Stereophonic Reproduction JAMES MOIR ':' A basic discussion of the reasons be hin d our ability to locate sounds simply by hear ing them , together with prac tical req uireme nts of stereophonic sound systems. HERE IS LITTLE DOUBT that the best from the movement of the sound source It is suggested that Chinn's preferred examples of current sound repro is irrevocably lost. frequency range tests using reproduced Tducer equipment meet most of the A similar result is obtained from a program material cannot be compared known criteria for a high quality monaural reproduction of the normal with Olson's tests using live matel'ial as monaural system and in consequence movement of actors about a set or stage. in the latter tests the audience were there does not appear to be a g reat deal Movement in depth is moderately we!l listening "binaurally." The difference in of opportunity for f,urther improvement reproduced if the reverberation condi conclusions largely represents the dif in subjective quality if present tech, tions are satisfactory but all movement lerenc.: between monaural and binaural niques are merely subject to g reater re across the stage is. reproduced as move reprorluction. fi nement. F or exampl e an amplifie:' ment in depth. T hus all the action ap It is appa rent that at the pl'esent time having a frequency characteristic flat to pears to take place in a tunnel with a few of the advantages of a stereophonic .01 db and a distortion content below microphone at its mouth . system can be expressed numeri call y .01 per cent is not sUbj ectively better Current microphone techniques aim and recourse mu 't be made to express than an altem ative design fl at to 0.1 db to hide this defect by such procedures as ing opinions until such time as we have (or even 1 db ) and a distortion content employing a mi crophone boom to sup some system of indicating the overall of 0. 1 per cent. In spite of this state of port t11 e microphone just out of the pic subjective appeal of a reproducer sys (pseudo) perfection no competent critic ture and over the head of the peaker tem, A number of organizations have would consider that the best possible th e standard fi lm and TV practice, wOl'ked on the problems of stereophony monaural reproduction of anything but A monaural system is at a further both in E urope and in A merica and have a soloist could be mistaken for the rea l di sadvantage in that a single mi crophone recorde,l theil' opinions on the advan thing, and until we can deceive most Ot is unable to discriminate against r00111 tages of stereophonic systems, the people for most of the time there is noise or reverberant sound, with the re Thus, tests by Ben Labs indicated room for improvement in techniques. sult that all recording and broadcast that a stereophonic system having an The pleasure derived from listening studios must be acoustically treated to audio bandwidth (per channel) of 3750 to a live orchestra is compounded of obtain a reverberation time much below cps was considered by an audience to many factors, most which are adequately that known to be optimum if a tolerable have the same aesthetic appeal as a dealt with by a laboratory type of resul t is to be obta ined with a monaural monaural system 15,000 cps wide. J. p, monaural reproducer system, but if we reproducer system, Similarly, noise from Maxfi eld of Bell Labs has stated "I a re to have a perfe ct re pro d't ~cti on of the the audience coughi11g and shuffling ap would rather hear a two channel repro original there are many marginal factors pear to be enormously enhanced when duction fl at to 6,000 cps than a single that require further attention. A n or heard over a monaural system. A simple channel system fl at to 15,000 cps; it is chestra generally occupies a' platform but remarkably sati sfying demonstration mOI'e pleasing, l1101'e realistic, more 60 to 100 ft. wide and 20 to 30 ft. deep of the magnitude of t11i s effect can be dramatic." This is a concise indieation and this spatial distribution contributes obtained by anyone with normal hearing of the writer's opinion after 1ll01'e than to the pleasure derived from listening. and access to a hearing aid of the noi' a year's work on the subject, with the There is merit in mere size. An or mal monaural type. Conversation that opportunity of heal'ing the systems de chestra that makes use of all the instru is easily understood and appears to be veloped by three of the leading E uropean ments all the time is fl at and unintel'est without any noti ceable background when concerns, ing and is ra rely employed .. Instead the using two ears, appears against a listeners interest is excited and main marked background of reverberation and Explanation of Stereophony tained by constant change in the prom other room noises requiring consider V/ ithout further di scussion of the vir inence g iven to the various instrumental able concentration if it is to be under tues of a stereophonic system, the combinations. Thus the centre of the stood when the monaural hearing aid is mechani sm of the stereophonic effect listeners' interest moves about the stage, used. Kock has shown that ilie human will be di scussed as 'this is probably the the remaining instruments forming a hearing mechanism automatically dis best approach to an understanding of t11e pleasant but unobtrusive background to criminates against noise when it ap technical requirements of a stereophonic the focal zone on which the listeners proaches the head from a dil'ection system. immediate interest is concentt'ated. whi ch differs from that taken by the Mother Nature has provided us with desired soun d, T his binaural discrimina two ears and these enable us to sample Reduction of Source Width tion in favor of the wanted sound the sound fie ld at two points spaced apart amounts to as much as 10 to 15 db , and by the width of the head, F rom the dif A monaural reproduction is com is entirely lost when a monaural system fe rences that exist at the two ears and pletely unsatisfying in t1::s respect, the is used, with the henefit of long experience. the whole of the 100 by 30 ft. source being A further and somewhat unsuspected ear - nervous system - brain combination compressed and strangled to emerge result of this binaural di scrimination is can estimate the position of a sound from an 8- or lO-in. diameter hole, w ith a marked increase in the clarity of source wi th remarka l--J e accuracy. giv the result that there is no possibility 01 speech and an apparent decrease in in ing the same three-dimensional signifi identifying or appreciating the incli termodulati ol1 distortion when repro cance to the acoustic env ironment as the vidual instruments or sections of the ducing music from a large source such possession of two eyes gives to the orchestra on the basis of their spatial as an orchestra. In fact it gives to the visual environment, di stribution. The pleasure to be derived reproduction of a large orchestra the For any sound source not 111 the degree of cl arity characteristi c of a small median p l ~ll1 e the sound at the left ear "87, Catesby R oad, R11.gby, Englalld. olThestral combinati on, will diffel' from the sound at the r ight 26 AUDIO ENGINEERING • OCTOBER , 1951 ear m three major respects. has adopted the first positive peak as 1. Referring to Fig. 1 it will be seen a reference point and that in measuring that a sound fl'om a source on the right time intervals to fix the position of a . I o~ 4 si de will strike the right ear before the sound source in space, it notes that -... left ear, the time difference being a interval between the first positive peak V~ b-... arriving at the left and right ears. This / maximum when the SO urce is on one .,,/ (/) 0 ~~) side anel in lin e with the two ears. In process must be I-epeated at fairly fre ..J quent intervals if a moving soutce is to this position the time difference IS ~"' - 2 ~ 1/ be followed and it is suggested that the FAR .00063 sec cor responding' to an ear ."'0 ',\ EAR separation of 21 cm. intervals between syllables might well - 4 ,, V fo rm the convenient gaps from which j..../ v,-,- -6 "- to commence each new measurement .. -- --- ,- SOUND SOURCE of "time of arrival"-difference. DIFFERENCE t-'- o 20 40 60 80 100 120 140 160 180 The loudness difference at the two ANGLE In DEGREES ears is mainly due to the presence of the head between the ears. Any obstacle Fig . 3. Variation in loudness as a speech source is rotated in a horizontal plane around t he 'placed in a sound field distorts that head. fi eld. producing an increase of pressure ~~lrE~~~giH '" ' AT EARS , on the side facing the oncoming sound source is then symmetricall y di sposecl ,r, wave and a decrease in pressure on the with respect to the two ears, a concl.ition reverse side- a process known as cli f that holds at all angles of elevation. It fraction. The pressure difference be is to be expected that the precision of tween the two sides is a function of the location in the vertical plane wouln be Fig. 1. Difference in path length and time of ratio of obstacle diameter to wavelength poor and in practice this is found to b.: arrival when sound source is not in median of incident sound; and for a ' given size the case. Discrimination between hack plane. of obstacle will increase as the frequency and front is also fo und to be poor unless 2. There wi ll be an intehsity differ of the incident sound rises (i.e., wave the head is free to make some explora ence at the two ears, this difference be length falls). An exact calculation of the tory movement. The slightest rotation ing a function of the frequency of the fi eld distortion is a problem of great of the head' pl-ovides adequate discrim sound. The intensity difference is fre difficulty but as we are only interested ination between front and rear, pre quency dependent as it is mainly the re in diffraction around a human head, sumably as a result of the brain noting sult of diffraction round the head. Weiner's measured results are sati sfac the direction of the change in the time 3. Most everyday noises have a com tory. These are shown in Fig. 2 ancl differences at the two ears. plex frequency spectrum and as the dif It will be seen that there are three fraction losses are a function of fre (/) 1I1ain differences in the sounds at the ..J two ears- a time of arrival difference, a quency the frequency spectrum at the CD"' ~. two ears will also differ. ~ loudness difference, and a frequency 2 5 chamcteristic difference. At present These differences justify further dis thel'e is no conclusive proof as to which 20 -51 cussion. The reason for the difference in of these provides the 'real clue to locali 5 time of arrival at the two ears is evi ,-\ ,. zation in practice. It seems highly likely dent and requires no further explana 0 I \ , that all three make contribution, w ith tion, but the question immediately arises 5 time and loudness differences providing as to which part of the sound-wave cycle - - '. the major clues. . . is accepted by the ear as determin ing 0109 1,000 10,000 FREQUENCV - CPS the time of arrival at that ear. On an Practical Stereophonic Systems impulsive sound having a steep wave Fig. 2. Ratio of sound pressure (in db) at ears Consideration can now be given to front it may be assunied that the arrival for an angle of 45 deg. to the source. methods of achieving stereophonic I-e of the wave front is recognized, but on production via an electrical reproducer AUDIO ENGINEERING • OCTOB/ER, 1952 27 D Fig. 8. Method of error measurement in t sound location tests. SOUNDPROOF WALL Fig. 5. A wall can be rendered sound trans parent if face A is covered with microphones connected through individual amplifiers to loud- speakers on face B. right-ear signals cannot be allowed to contaminate each other. At the trans mitter end the sound pickup consists of two high-quality microphones mounted in a space model of the human head to If the li stener's ears cannot be trans ing the A face with a, large number of simulate the acoustic field distortion ported . to the studio it is possible to I11crophones each connected tl11"ough an produced by the head in practice. After adopt the alternative approach and amplifier to a loudspeaker on the B face amplification the .signals are conducterl ~tr arlspo rt the acoustic field to the list of the wall. Any sound field approaching by two 'sepaLate channels to . the '- t~6 :' ·.e neL - T he principles involved wi ll be the A face would be reproduced on the earphones. 'tfi:e results of this' are ex- ' dhdei'stood by referring to F';g. 5 show B face and the audience in the B section tremely ' iin~pl-e ss iv e , but the necessity of ' , ing a long hall divided into two sep'arate would be unaware of the dividing wall. wearing headphones militates against its sections by a soundproof transverse wall While this procedure would be reason use and it would appeal- unlikely to !'ind at A. This wall can be rendered sound ably effective it is commercially imprac favor with the general public .unless the transparent (unidirectionally) by cover- tical, as a sepat:ate line and amplifier are required between each microphone and its associated loudspeaker. Some means SOUND SOURCE of I- educing the number of miCl:ophones and loudspeakers is required. In the vast majority of stage plays and most film s the action is largely concen trated at ground level and as localization in the vertical plane is rather poor in any case it seems reasonable to assume ---- Fig . 6. Path-length that the "vel,tical" information need not /' discrepancy us i n 9 be transmitted. This eliminates the need /' -- /' closely spaced micro for aJl the loudspeakers except the .bot / phones and two- / tom row, a very considerab1'e simplifi / speaker system. cation. With present techniques two or PATH LENGTH / three separate channels are all that can DIFFERENCE TO MEMBER OF be accommodated on tape, disc, or film, AUDIENCE , so it appears advisable to check the per formance of two- and three-channel sys tems. In a simple two-channel system, local ization is weakest in the center just LISTENER where it is desirable that it should be at headphone cords are dispensed with. its best and the addition of the third This could be accomplished by intro [Continned 0 11 page 69 ] ducmg two local ( domestic) low-power radio transmitters with miniature l- e ceivers mounted on the headband-a pro cedure fairly common in film and T \T o studios for transmitting instructions to B \. /~ I the operators of mobile cameras mon A } 5 " I aurally. / \ I C LOUDSPEAKERS -10 Fig. 9. Filter charac J I teristics. (A) low " -1 5 I I STEREO EFFECT IS . pass filter; (B) band , POOR IN SHADED pass filter; and (C) I AREAS high-pass filter. -20 I I r I - II -25 I 30 , Fig . 7. When close-spaced microphones are ,. , . , , , .0000 ' .' 100 1000 10000 with loudspeakers, the stereo effect is limited FREQUENCY IN CYCLES PER SECOND to the clear area. 28 AUDIO 'ENGINEERING • OCTOBER , 1952 Design .fo r Clean ·Bass EDWARD J. GATELY, JR. ';' The search f~r .bet~er loudspeaker enclosures centers around improvement in low frequency radIation In small spaces. The author presents a simple and effective design. I-IE ~ f ODER N TREND towards extension of reproduction into the upper limits Tof human hearing sounds thin and shrill if a corresponding extension of the bass range is not made simultaneously. There are man.y methods of extending bass reproductIO n, but most of these have inherent di sadvantages and give rise to fa lse'or syntheti c bass and annoy ing boom. Fig . 1. Images of horn-mouth opening Truest reproduction has been accom effectively multiply plished only by the use of large ex actual opening when ponential horns. This is because the ex speake r is corner r------1--, mounted. I ponential horn acts as an impedance I I, M matching transformer enabling the loud I Is I speaker to set in motion the large f------I I I amounts of air necessary fo r true re L ___12 I, I production. The exponential h 0 r n - --' greatl y reduces the motion of the loud speake!-, thus reducing distortion and in creasing the power handling ability of ~:i : , ~~ n~ ~E~E I~MC~GRENSE~ FO~H~~~R~ ' the speaker system. MO UTH , M. At low frequencies a loudspeaker op erates as a constant velocity transducer. That is, fo r constant radiated power, horn axis has been developed to overcome all these the velocity of the cone remains con A" = area of 'throat of horn di ffi culties and sti ll meet all the above stant as the frequency is halved, but the -,I; = distance along axis of req uirements of a true horn. By oper ampli tude is doubled_ In the lower audio horn ating a horn where three mutuall y per spectrum extremely large amplitudes are 4rrf" . pendicul a l- SUI- faces intersect such as in til =. --'constant denotmg required to radiate even small amounts o the corner of th e room, the wall s and of power. These large amplitudes give taper rate of horn fl oor (or ceiling) act as an extension ri se to distortion due to the non-linear fa = cut off frequency of of the horn mouth giving rise to suspensions of the cone and non-li near horn images 111 12 , 13, I., and 15 ( See p.':g . 1) . fl ux densities in the' air gap. A horn a = veloc ity of sound in air T hus, the effective mouth a rea equals greatly increases the air loading on the six times the true mouth area. T he mouth a rea of the horn should co ne and reduces the amplitude the cone T he construction of the Super H om must travel to radiate the same amount equal approximately the area of a circle whose diameter is l i n; times the wave is such that panels 1, 2, 4, and 5 act as of power. This materially reduces di s an exponential horn following a true tortion. length of the lowest frequency to be reproduced. exponential within one per cent. (See A true exponential horn is a passage If we 'desire to make a true horn with Figs. 2, and 3). The throat of the horn way whose area doubles along discrete (T ) is fornled by the top edge of panel an 80-cps cut-off, then the rate of taper increments . of length. T wo factors gov should be such that the area doubles 2, and panels 4 and 5. T he mouth ( M ) ern the succes of a horn operated at low every 9 in. , and the mouth should have is defin ed by the bottom edge of panel 3, hcquencies. F irst, the taper of the horn the bottom edge of panel 1, and edges an ·a rea of approximately 2110 sq. in. should be such that the pI'opagati on of If we desire to operate this horn from of panels 4 and 5. V a acts as a coupling low hequencies thwugh the horn is ac chamber to keep high frequencies out of a 12-in. driver having an effective cone co mpli shed easil y. F or good low-he the horn. and indicate the di s area of 75 sq. in., then the horn must Xl X 2 quency reproducti on, the taper should tance over which a rea of the horn dou ,be nearly 4 ft. long. If a lower cut-off be very gradual. Second, the mouth area frequency is desired, then the taper will bles. The a rea at Q is double that of the of the horn must be adequate if smooth throat and the area of the mouth is dou be slower and a larger mouth area will response is to be realized. If the mouth ble . that of Q. Once a fl are-rate is be req uired, and the length will be chosen, the rest of the dimensions of the area is inadequate, refl ections occur at greatly increased. Thus it is easy to see cabinet may be determined geomeh-i th e mouth and the response tends to that straight horns are impl-acti cal fo r resemb le a picket fence. T he above cally. home use. Many ingenious methods of criteria may be expressed mathemati folding horns have heen developed. hut Two models of the Super Horn are call y as the complexities of construction have presently ava il able. One designed for A = AnE""" made them relatively expensive, and the 12-ill . speakers has a taper rate to give where A = area at any point along maintaining of an optimum mouth area a 78-cps cutoff and has an effective has made these types of units too large mouth a rea of 1728 sq. in. This satisfies very closely the above requi rements of * Gately DlTuelopment La.bo·rato·ry, B o.'!; 2, fo r home use. Clifton H eights, P a. The Super Horn (patent pending) [Continu.ed on page 92] AUDIO ENGINEERING • OCTOBER, 1952 29 Planning and Building a Radio Studio EUGENE F. CORIELL ':: Major, USAF Part 5. Concluding this series with the fin ish ing touches on wiring and cabling, a discussion of groun ding, an d suggested tests upon completion of the installation. HE PRECEDI NG I.NSTALL1v~ENT covered resulting when, for example, the shield six of the audio plannmg steps m of a cable pair is grounded at both ends. Tstudio des ign. These were : 4. Rack It will be noted from Fig. 2 that multiple layout; 5. Relay systems; 6. Rack in g rounding forms a coil of one turn, in ternal cabling layout; 7. Interconnection which a voltage may be induced by any cabling layout; 8. Cable list; and 9. nearby a.c. field. Since the pair shield IS Audio conduit diagram. The remaining" part of the loop or tum, noise may steps will be discussed in this final in thereby be induced in the conductOl'S . Fig. 2. Ground loop result ing from grounding stall ment and include: 10. Grounding Another g rounding principle is to ti e shie ld to chass is at both ends of pair. diagram ; 11. Running sheets; 12. Inter together the racks and the console connection sheets, and 13. List of con chassis with a heavy ground conductor, struction materials. There will also be a insulated # 10 or larger, which is run to the reasoning holds nevertheless. Such br ief di scussion of the testing of the station ground. It is sometimes neces grounding between racks and console newly-completed audio system. sary to slip a bare copper brai d over this also reduces capacitative effects between units, and cuts down r.f. pick-up. A third-but very tentative-rule is TB2 to ground the shi eld of the input pai r REMOTE . 1 to the amplifier chassis; the shield of the DI VID ING PAD output pail' should be grounded to the T B 2 f ·2B ja;j TA PE~ frame or chassis at destination as shown :~I"1R 'C' 11 5 37 "'5::': in Fig. 3. This works out well in imple " ~RG systems but is not a lways practical in ~ DI SC more compl ex layouts, or ",hen jack ~ 'rt tt~ fields are involved. Jack frames are usually bonded to gether and grounded to the rack itself which in tUnl .is tied to studio g round. CONSOLE One I'eason for bonding the jacks is to CONDUI TS LEGEN D __ 0 __ reduce capacitative coupling between SHIELD WR WALL RECEPTACLE circuits. Anothel' reason is to permit the T B TERMINAL BLOCK shields of all pairs within the rar:k to be RG RACK FRAME GROUND grounded to their respective jack frame. SG STATION GROUND (Fig. 1) This avoids the complexity of -'-<> PATCH or CONN ECTO R COR D calTying all the shields through the rack terminal blocks (while keeping the Fig. 1. Portion of the grounding diagram for the sample studio illustrated in this series. Note shi elds insulated from each other) for t hat no shields are carried t hrough the terminal blocks. Shields of pai rs in rock are grounded eventual grounding at the console or . to their respective jock fromes which are bonded to the roc k. Shi elds of poirs coming to rock f rom consoles a re grounded to console. Note also (inset) the separate ground ing conductor elsewhere. The same advantage appli es which t ies conduit, rock, and console together and goes to station ground. All rock amplifie rs when rack connections are made to the (not shown) have t heir chassis grounded to ro ck. console through separable Jones plugs in stead of fixed terminal bl ocks. I t is Starting with step 10, a good ground wire and g round it to stati on g round, essential, of course, that g rounding in ing system should reduce noise and hum, Such a conductor does several things. It structions appear on the running sheets r.f. pick-up, high-frequency oscillation eliminates the temptation to use the and interconnection sheets for the guid or singing, crosstalk, and danger of elec shi elds of the intel'connection cables as ance of th e wi reman. trical shock. Since improper g rounding inter-rack grounding bonds, with result may increase one or more of these haz ing ground loops. It also reduces the ards, the grounding system should be danger of shock from the building a.c. planned as carefully as the audio wiring service, which always has one side itself and should appear in detail on the grounded. Section 2541 of the 1951 grounding diagram, Pig. 1. National E lectric Code !3 tates: "Exposed The basic rule of audio g rounding is, conductive materials enclosing electric of course, the familiar precept: U se one equipment, or forming part of such point grounds to avoid the ground loop equipment, are grounded for the purpose of preventing a potential above g round Fig. 3 Grounding arrangement for very simple * Radio T echnical Officer, A1'med Forces system. Sh ield of input pair to each amplifier Information School, Fort Slocu.m, New on the equipment." While this section is grounded t o that amplifi er. Shield of output York not directed specifica ll y at audio racks, pair grounded at destination. 30 AUDIO ENGINEERING • OCTOBER, 1952 Guard against g round loops from duits. Some enginee l- s prefer to show anced systems is best determined by patch cords by making sure the shields the g rounding arrangements on the trial ; this puts a premium on accessi al-e g rounded to the plug body only at block diagram itself. It has been the bility of such ground connections after one end of the cords_ Also look out for writer's experience that superimposing , install ation. unexpected loops resulting from capaci complete g rounding data on the block T he g rounding diagTam a~'so shows tive coupling_ Even a turntable motor diag ram seriously impa irs the legibility the various level-g roup fami1i es of con housing may show considerabl e capaci of both. H owever, a spare copy or print duit connected to station g round. These tance to nearby a _c _ circuits_l E xperi of the block di agram can be used as a conduits should not be grounded to the menting with various g rounding points work sheet on which th e g rounding can building a.c_ conduit. H owever, the haz will usuall y help this condition_ This be worked out by cut and try. T he layout ards of constr'uction often result in such can then be redrawn in whatever form po ints up a construction precaution for grounds being. not removable. In such seems best. The g rounding diagram in whi ch the wri ter, at least, has always cases, the audio g round may have to be F ig. I somewhat resembles the block di a been g rateful : P rovide fo r permanent remo.ved from the conduit and should g ram but is to larger scale, includes tel- thel-efore be readily accessible to the access to all g rounds_ S ince g rounds minal blocks and grounding notes, and technician. must sometimes be added as well as re moved, it should be possible for a tech LEVEL GROUP : LOW nician to reach the ends of all cabl e RUNNING SHEET SHEET t OF 9 SHEETS STUDIO 'C' shi elds and other probable g round points without tearing out adjacent wiring_ T o NOTES: RED MEMBER TO R.~ . TI P SEEN FROM REAR , AND TO ODD NUMBERS 'ON TERMINAL BLOCK "x" DENOTES SH IELD GROUNDED TO FR AME, CHASSIS, OR BUS INDICATED facilitate thi s, it's a good idea to leave TB · TERMINAL BLOCK a pigta il taped up on the ends o! pair shi elds not originall y planned to be PAIR CAB LE CIRCUIT FROM TO SKETCH CHECKS NO . LETTER NO. g roun ded_ EQUIPMENT TERMINALS EOUIPMENT TERMINALS I B MIC. • JACKI X 1,2T TB I 1,2 JACK I 3,4N JACK13 3,.4N R_ F. Interference 2. B MIC. 2 JACK 2 X '1 12T TB I 3,4 R f. pi ckup can be a most annoying . JACK 2 3,4N JACKt4 3,4N 3 B MIC. 3 JACK 3 X i.2T TBI ' 5,6 phenomenon. By r.f. is meant not only I JACK 3 3, 4N JACK 15 3,4N electrical machlll ery interfe rence such as 4 B TTl JACK 4 X 1,2T TB I 7/3 motor and generator commutator spark JACK4 3,4N JACKI6 3,4N 5 B TT2 JACK 5 X TBI ing, but also the sig nal from nearby 9 t tO JACK, 5 ~~~ JACKI7 3,4N broadcast transmitters. A nd it doesn't 6 B LL ANN . BOOTH JACK 8 X -1,2 T TB I 11,12 I matter whether the transmitter is yours UTILITY., 7 B LL ANN. BOOTH JACK 9 X 1,2T TBI 13,14 1 or a competitor's. The writer recall s a UTlLlTV.2 · studio near a super-power transmi tter 8 B LL,TRUNK .. t JACKt2 X 1,2T TB I 15,16 2 antenna wherei n not only the in stalled TO MIC. L..-- ____ l..-----"'-- audio equipment but also the portabl e - tape recorder, the intercom, and even the p. a. system gave fo rth with th e Fig. 4. Sample of typical running sheet for audio cables. proo- rams of our giant neigfiboL The tr o l~hl e is due to the low-lev el lines L£ vn GROUP : LOW SHEET '1 OF 4 SHEETS INTERCONNECTION SHEET from mi crophones, turntables, etc., act STUDIO ·C· ing as antennas and feeding Lf. energy NOTE~ : RED MEMBER TO MIC. AND TT RECEPTACLE II I to the audio gear where any one of sev "x" DENOTES SHIELD GROUNDED AT TERMINAL INDICATED eral conditions causes rectification. In TB " TERMINAL BLOCK; WR . WALL RECEPTACLEj RG" RACK GROUNO; MeG. MASTER CONTROL GROUNO aggravated cases, the resulting speaker output over-rides the des ired signal. PAIR CABLE CIR CUIT FROM TO SKETCH CHECKS NO. LETTER EQUIPMENT TERMINALS EQUIPMENT NO. There a re several solutions or parti al TERMIN ALS sol utions, in addition to the usual audio 1 J MIC.I TBI 1,2 WRI _"t,3 (2X) grounding procedures and precautions. 2 J MIC. 2 TBI 3,4 WR2 t,3(2X) 1. Keep a.c. power and low-l evel input circuits as short as possible_ 2. Orient the 3 J MIC. 3 TBI 5,6 WR3 1,312XI a.c. power plugs for minimum pick-up. 4 J TTl TBI 7,8 ' WR4 1,312X) 3. Use d . chokes with or without shunt ing capacitors between low-level sources 5 J TT2 TBI 9,10 WR5 1~3 12X) and their preamplifiers. 4. Connect a 6 J LL ANN. BOOTH TBI U,t2 ANN. BOOTH 1,3 I capacitor and/ or a resistor between UTILITY. t I RG-X) WRf ' chassis and one end of either the pri 7 J LL ANN. BOOTH TBI 13,'14 ANN. BOOTH 1,3 I mary or secondary of the preamplifier UTILITY.? IRG- X) WR2 MC-TB-'3 in put transfonl1er, but check the eff ect 8 J LL ~~U~~ *~ h TBI 15,16_ l~t~~X) 2 on the hi gh-frequency response. 5. Insert h L-- a I : I isolati on transformer ( having electrostatic shield between windings ) Fig. 5_ Sample of typical interconnection sheet. This carri.es on ~o their '.destinatio ns the rack between mi crophones or turntables and circuits shown on the running sheet, Fig. 4, as terminated In Terminal Block #1. thei r preamplifiers_ 6. Replace preampli Illay show transfo rmer windings where Care must be taken in regard to the fi er input tran 'former with one having necessary. The g rounding layout illus microphone, turntable, and other low an el ectrostatic shield_ 7. U se a g rounded trated also includes an inset showing the level circuits. The cable should, of bare copper braid as a second shield g rounding coi1ducto: between r a c~ s and course have insul ation over the shi eld over low-l evel pail-so 8. Build a g rounded console_ I t is essential to keep thiS con which' should not contact the conduit copper-screen box around preampli fie rs ductOl- in mind since decisions as to at any point. Noise and hum in such and turntable filters. which shield is g rounded wl1ere must be cil-cuits can sometimes be reduced by based on its existence. The g rounding Grounding Diagram using the gro).lnd wire in the conduit . ystem illustrated assumes all amplifier ( suggested in the previous installment) There should be a layout of the entire chassis in the racks are firml y bonded to place a ground on either the shield grounding system, including the con- to the rack shell , and that all circuits are or the conduit at destinati on. balanced to ground. In the writer's I Olive r B. Read, "Rum-dill g and R ep·ro [Co ntinued on pa ge 74] dll elion of Sound" (2nd Edition), p_ 670. opinion, the proper grounding of ,§~nhal- 31 AUDIO ENGINEERING • OCTOBER, 1952 \ A Corner-Mounti ng Infinite Baffle M. V. KIEBERT, JR. ':' A presentation of some of the problem s- Involved in loudspeaker enclosures for high-qua lity re productiori?,>arnd the author's solu tion with a su itable design to house an LC-l A speaker mechanism. AST EXPERIEN CE has all too often neering business dictates, a brick or els and hence comparable dynamic made us painfully aware that what stone enclosure thus bei ng ruled Qut, ' ranges, Consideration was given to the P was oft<;!n called a "loudspeaker" In casting about for a suitable device effect of monaural li stening as compared "vas just exactly that and not the "repro it is immediately apparent that there to binaural listening and to the aural dis ducel'" that it should have been, wel'e but two basic design paths to fol crimination intrinsically present when In order to attempt to satisfy a very low; the horn-loaded unit, and the di sight is used to supplement sound, critical listener who happens to be a rect-I'adiator system, With monaural listening it appeared rather exacting engineer by profession The problem of power output was that an acoustic level of one to two and an out-of-hours musician by hobby, next considered,. Measurements of the acoustic watts could do a satisfactory but who knows what he likes when it acoustic power levels of the various in job, but that an additional 10 to 20 db comes to musical reproduction, a survey struments were rev iewed; a sound-level of dynamic range would be desirable, was made of the over-all reproduction meter was used to survey typical levels The measured dynamic ranges of direct problem, Seven years of test, explOl'a encountered at choice locations at sev . (live concert of the Philadelphia Sym tion. and development followed. Not eral Philadelphia Philharmonic and phony) performances were surpris only was it necessary that it must not Lewisohn Stadium concerts, -ingly low (presumably because 'of the offend the eye, it was also required that Noise-level surveys at these concerts averaging due to reved)eration in the the as embly shoul d be capable of being were also made and compal'ed with typi hall). Twenty to twenty-five db ap moved from pla-ce to place as the engi- cal home li stening levels in order to as peared to be a maximum. sess more accurately a scale factor This study provided initial clues as to * Eel-ipse Pionee?' Division, Belldi.1; Avi which would provide equal desired-sig the requil'ed optimum design trends. ation C m'p" T eterbm'o, N , J, nal-plus-background to background lev- Early experience with theatl'e horn and theil' 20 to 25 per cent conversion effi ciency, indicated that an amplifier with a clean 4,5 watts of electrical output would do a good job covering 600 to 1500 people, Typi2al dil'ect radiator svs tems have conversion efficiencies of 3- to 16 per cent so the power amplifier must have between six and thirty electrical watts output to do the same job in a sati sfactory manner. From our point of view the low-effi ciency, power-dem.anding;· dil'ect-radi ator system is not good design. The lower efficiency units generally are that way eit.her. because of inadequate mag netic CirCUits, or as a result of dia • phragm break-up- both being cases to Fig, I , A simple yet he avoided if 1M is to be kept to a low n e at appearance valve. The higher more efficient di rect characterizes the au radiator units such as the Altec 604C thor's spea ker en or the RCA LC-IA pei'mit a good de closure which pro sign compromise by only requirino- a vides fo r a 15-in . nominal six- to twelve-watt power ~m single-unit speaker plifier which is relatively easy of at mechanism . tainment with low-voltage, low-cost power supplies and rather nominally • rated and operated powel' output tubes, Fr ~ quency Range The next item for consideration was frequency range and the sound distribu tion patterns desired 'for average instal lations. Many engineers and· hobbyists rather indi scriminately add high-frequency and low-frequency units into a system and frequently do achieve some measure of frequency balance insofm' as level as a 32 AUDIO ENGINEERING • OCTOBER, 1952 function of frequency IS concerned. However from the writer's point of view this procedure would be analogous to having an artist paint a background in one picture, the theme or object in another, and the high lights in a third. Then by hanging all three pictures side 6 by side we should get the integrated ~~ 29%------1 Jg(9'/4 r>- Whole. Leonardo Da Vinci didn't do it y IY - so we're not trying to do it either. Considerable experience in the design 6- of directional antennas (which may be likened to acoustic radiating systems) 1~ em phasized the distorted spatial distri I~ bution patterns that always occur when space separation exists between two ~ ",-'!! 2 .. sources of radiation even when these are t 241/2~ in phase. Add some phase variation and I· the spatial pattern becomes all the more non-uniform. From the foregoing it appeared that .l...-" horns and multiple-unit systems were ~ I·X 2" not too desirable and in fact critical ALL MEMBERS EXCEPT I 41/~U J CENTER POST li stening tests by musicians and non U musicians always seemed to favor the Fig. 2. Constructional details fo r the corner- mounted infinite baffle. single-source direct-radiator svstem when this was given A-B comp ~ ri so n For our requirements a corner inforcing reflection paths which might tests with multiple-unit horn-type sys speaker held several desirable advan otherwise degrade the response curve. tems. During these tests the observers tages. The corner design improves the The unit is mounted near the top of the did not know which system was in op radiation characteristics, as is well cabinet in order to provide the optimum eration. The almost universal response known ; the triangular design permitted spatial distribution with the sound was that one system seemed "smoother" very rigid construction; the des ign source as close to ear level as poss ible. The interior is lined with ozite ce than the other. easily permits asymmetrical speaker One axiom in enclosure design is this : mented on with rubber cement. Addi mounting and consequent avoidance of tional absorption was utilized by drap if when you touch the enclosure you spurious peaks, and the system pre can feel the low notes, it's not good! in g strips of ozite across the internal sented a minimum decoration problem cross-bracing members as shown in G. A. Briggs of Wha rfedale got in sofar as integration into a li ving space around this di fficulty by using a bl-ick Figs. 3 and 4. enclosure. John V. L. Hogan minimized was concerned. The performance of this speaker this difficulty in an early (around 1936) With a low-freq uency cone resonance mechanism in this particular cabinet is \iV QXR receiver by heavy cross-bracing of between 35 and 40 cps, and a desire considered adequately rewarding for the of the enclosure. The greater portabil to minimize the rate of roll-off below work involved in designing and con ity of the latter arrangement appealed this resonance as well a'S to ensure structing the enclosure, and it is felt to us and according this design proce smooth low-frequency curve immedi th at the complete system is as good as ately above it, a volume of approxi dure was foll owed. the writer can make it-until the urge mately 15 cu. ft. was decided on, and to . redesign shall again arise to stal-t a corr?pletely enclosed structure was con the entire cycle over again. sidered essential. Fig. 1 is front view of the enclosure. Construction In order to fit snugly against the wall, three legs 4y,1 -in. high were used in or der to raise the cabinet above the avel- age baseboard. This is not too desirable because of the small resonance peak oc casioned by the cavity formed between the enclosure and the floor. For this reason the legs are removable and we ultimately visualize installation of the enclosure against the ceiling. The enclosure is made of }Is -in. ply wood with construction details as shown in Fig. 2. Assembly is with wood screws and casein glue with particular care taken to insure a rigid and air-tight' as sembly. All peripheral and cross brace stiffen ers were made of 1 x 2-in. fir. The top to-bottom member was 2 x 2-in. fir tied into the three sets of interior cross· braces by cemented-in blocks aided by wood screws. The speaker mechanism chosen-the Fig. 3. Internal vi ew with one back panel re RCA LC-IA, more commonly known as Fig. 4. Sfrips of Ozite lining are draped moved to show cross bracing and unsymmetrical S~rap over internal bracing to further dampen the mounting of the speaker. Also note start of the Olson speaker-is mounted asym cabinet. Ozite lining in lower part of' cabinet. metrically in order to break up all re- AUDIO ENGINEERING • OCTOBER, 1952 33 I The Violin ALBERT PREISMAN ':: Part 2. Continuing the discussion of one of t ~ e most important instrumen!s in music. This installment covers the bas ic construction of the body of the Instrument. N LAST MONTH'S install ment, ~he his The E string is located over foo~ A. between the string and the belly of the tory of the violin was d:scussed When it vibrates, it causes the bndge violin is impaired, particularly for the I briefly, and some of the l?aslc char to rock, presumably on foot B as a higher frequencies. At any I:ate, the ton.e teristics of the tone-produc1l1g . o~en~ fulcrum, and the foot at A causes the is dull and "sluggish," which means It tion were described. While the v~oll11 ~s belly of the violin to vibrate, because tl~e lacks hio-her frequencies. On the other apparently an . ~nstr u ment which IS belly here is more nearly resonant to thiS hand th; tones are faid y loud. reasonably famlhar to most I ~ym~n, rano-e of frequencies. W ith regard to If the bridge is too low, the .ton~ is many will be su!"prised a~ the 1I1tncaCIes the "A and D strings located in between not as loud, but is harsh and plercmg, of its constructIOn. It will be seen that which means that the higher harmol1lcs the G and E strings, the probability is are unduly accentuated. It is said that a this instrument is not just "a cigar box that the fulcrums are somewhat less high bridge accentuates the faults m a with a handle on it." clearly defined, and both feet rock and cause the belly to vibrate to some extent The Br idge beneath them. In short, the bridge is not a well-defined bell-crank lever, and is Figm'e 5 shows the shape of the probably caused to rock more or less bridge as finally dete.rmin7d by Stradi on both feet, depending upon the fre- varius. The name bndge IS very apro quency involved. . . pos, for it acts as a brid~e over which The incisions in the bndge, shown 111 the vibrations of the stnng may pass Fig. 5, undoubtedly introd,~c~ 34 AUDIO ENGINEERING • OCTOBER, 1952 sound of the instrument is found to throb. However, if the difference is greater than one tone, the results are said to be even more unsatisfactory. More will be said about this presently. ~ BASS BAR The thickness of the wood is import - ~-= ant. It must not be too thin, otherwise the tone is weak and feeble. This de pends, however, on the shape. The old q-LENGTH OF VIOliN ~ German violins were high-breasted (highly arched), which made their top - and bottom structurally stiffer. In order ~ to have the correct pitch, the wood had to be made thinner. In this case the main ,. disadvantage is that the instrument tends to be . too weak to withstand the pull of the strings. This, by the way, corresponds to a total pull of 68 pounds, Fig. 7. Side cross-sectional view showing t he bass bar. and the vertical pressure on the bridge is about 26 pounds. Yet the entire violin quency. This effect compensates for the tions are prevented by the stiffening weighs but 8Y;; ounces! lowering of the stiffness and hence action of the bass bar. If the wood is too thick, the tone is natural frequency of the belly when the It is for that reason that the bridge sluggish and dull, which indicates sup i-holes are cut; the bass bar restores was stated to rock about the right foot the natural frequency back to approxi pression of the harmonics. Nevertheless, for low-frequency vibrations, and about a violin with thicker wood will develop mately C, or 512 cps once more. It also the left foot for high-frequency vibra prevents segmental vibrations of the in time with continued playing, and will tions, for in either case the other foot wood in this region, in contrast to the probably withstand the ravages of time finds the wood it is resting on can sound post. more successfully than a -violin made of "give" and vibrate at the frequencies to The sound post is a )/,i -in. rod or thinner wood (within reason, of course). which it is approximately resonant. dowel of white pine, which ·is inserted The body encloses a certain volume We note that a poor violin is often vertically as a kind of prop inside of improved by placing the post nearer the of air, which must be correct so as to the body between the belly and back of bridge, although it requires very careful resonate at the proper fundamental the violin. As is indicated in Fig. 8, it playing to render the tone even. On the frequency. This corresponds to about rests in a line with the right foot of other hand, if the tone is even but rough 300 cps, which is in the range of the G string. the bridge (directly below the E string). and harsh, the post must be moved back Actually it is set about )/,i -in. behind or a little (thereby presumably de-empha The comments of musicians concern below the foot of the bridge, with its sizing the higher frequencies). ing the proper volume is of interest: grain at right angles to that of the belly. If the high strings are weak and the If the air volume is too great, the low This is perhaps the most important low ones are harsh, the post should be notes are weak and dull- and the high element in the instrument; upon its set moved a little outwards toward the notes are sharp and thin. If the volume ting and thickness depends the tone of i-hole. If the low notes are weak and is too small, the low notes are coarse the instrument. In the first place, we the high ones shrill, the post should be and those of the E string lose their note that it is not glued to either the moved slightly toward the center. . brilliancy. We note, in passing, that in belly or back, but merely wedged be It is possible to simulate the actIOn the case of the cello, the depth is rela tween the two. As such its action ap of the sound post by pressing with a tively greater thrul that of the violin, in pears to be similar to that of the finger weight on top of the belly, as was dis order to avoid too large an instrument. on the string when playing a harmonic ; covered by Professor Savart, a famous When the body is glued together, it the finger is pressed lightly so as to es French investigator of the violin. This shows a strong 1·esonance peak around B tablish a mode for the desired harmonic indicates its nodal action in the violin. flat on the A string. This can be dis and to kill any fundamental vibration of Perhaps one of the most striking fea tress ingly strong, in which case it pro the string. tures of the action of the sound post is duces a tone that varies cyclically in In the same way the sound post ap that it deadens the sounds of plucked intensity, and is known as a "wolf note" pears to fo rce the wood to vibrate in strings (pizzicato). For that reason it from its ululant nature. Cellos are par segments such that where it presses is absent in the mandolin and guitar; ticularly plagued by this . phenomenon. against the wood a node is established. this is perhaps as important a difference Experiments by Kessler indicate that Thus the right foot of the bridge rests between these instruments and the vio it corresponds to a particula rly strong on a part of the belly that is constrained lin as their method of being energized, mode of vibl'ation of the pine belly of to vibrate at the hi gher frequencies by that is by plucking rather than by being the instrument, with one node coincid the sound post, whereas the left foot bowed. ing in par.t with the bass bar under the rests over the bass bar where a lower The final important feature of the G string, and another node under the natural frequency of the wood occurs, body of the violin is the i-holes. These E string and passing through the sound and segmental higher-frequency vibra- - [C ontin1!ed on page 67] post. Elimination of the wolf note is not easy; in the case of a violin it is a fairly sharp peak, and if it can be made to fall between two adjacent notes of the • instrument, it will be less objectionable. In the case of the cello it unfortunately is a broad resonance peak and ·embraces Fi g. 8. Cross-sec approximately four notes, so that its t io nal view t hrough elimination is exceedingly difficult. t he midd le of the Directly under the G string, and run violin, showing sound post and posi tion of SIDES or RIBS ning for lO Y;; inches of the l eng~h of t he bass bar. SIDES or RI BS the instrument, is the bass bar, Ftg. 7. It is made of pine, cut to fit the contour of the belly, and glued to its under s~de. Its action appears to be that of addmg stiffness to the belly along its line of • contact and therefore to raise its fre- AUDIO ENGINEERING • OCTOBER, 1952 35 Handbook of Sound Reproduction EDGAR M. VILLCHUR ':' Chapter 5-Musicallnstruments and the Human Voice A discussion of the methods by which sound is produced by various familiar musicai instruments. The author shows how air is set in motion by vibration of some part of the sound producing device. OST SOURCES of musical sound, in has a saw-toothed wave shape and is ap cluding the human voice mecha plied over a very small part of the total M ni sm, are complex systems, con length, causing a deformation far differ taining a primary vibrating source plus ent from that which would be associated a system of resonators and acoustical with a pure sine-wave fundamental vi couplers. The primary vibrating element bration. The multi resonant properties of -reeds, strings, and air streams flipping the string create a pl'imary tone with back and forth across · hard edges are strong harmonics which reach into the common types-pl'ovides the initial osci l higher orders. latory energy for the fundamental tones The various intercoupled mechanical a nd a spectrum of harmonics. In the case and acoustical resonant systems of the of the triangle, the cymbal, and a few body of the instrument respond to this other percussive instruments, the pri stimulation rich in harmonics, produc mary source comprises the entire system, ing a tone such as the typical violin but ordinarily this source is coupled to wave form illustrated in Fig. 5-1. The and partly controlled by resonators be lly, back, and ported enclosure serve a which selectively emphasize certain dual function as resonators and as a ir harmonics and g ive the sound its charac couplers. teristic timbre. The majority of instru Although the resonator formed by the ments, with the notable exception of enclosure and the f-holes (so named be members of the flute bmil y, also have cause of their traditional pattern) is of a sO'unding board or horn to increase the the Helmholtz type, without overtones, efficiency with which oscill atory energy it is highly damped due to the viscosity is coupled to the air. of its internal surfaces, and it tunes A The various instrument families will broadly and reinforces the tone of a be di scussed along the lines of the gen large band of frequencies in the lower eral functional breakdown indicated range. In addition the dimensions of the above. body relative to the wave lengths of the sounds produced is such that various air The Bowed Strings column resonances also come into play. j 2 3lilllMld 4 5 6 1891 2 J 4 T he primary vibrating source of a The di stribution and relative strength 200 1000 bowed string instrument is the mechan'i g iven to harmonics are what determine cal mass-elasticity system formed by a the difference between a high-quality B stretched string, wh ich is normall y set I11strument and a poor one. into vibration by drawing a rosin-coated If the main body resonance is a sharp Fig. 5-1. (A) Wave form and dominant har ha ir bow across it. The bow tends to one the instrument may vibrate so vio lently at the c;orresponding frequency monies of typieal violin tone at 196 cps. (B) drag the string along with it, and suc Relative intensity, in db, of components of the ceeds in displacing it transver ely unti l that it produces a very unpleasant howl ing effect called the "wolf note." Meas tone. (Courtesy McGraw-H ili Book Co. from the elastic restoring force of the ystem Psyc hology of Music, by Carl E. Seashore.l exceeds the frictional coupli ng between ures taken to counteract this effect in bow and string. At this point the string clude damping and careful adjustment 1 molecules must be increasingly g reater, is released and springs back, and the of the resonant frequency of the body. There is a clear parallel between this for the same sound power, as the fre bow does not catch again until the string quency of vibration is decreased. Since has exhausted its momentum in the op difficulty and simil ar troubles . occurring in loudspeakers. the vibratory excursion of the in stru posite direction. ·Since the friction be ment's belly and back is obviously tween moving surfaces is less than that The design differences between the different members of the bowed string limited, the radiation of sound power at between surfaces at rest with respect to low frequencies is kept up by moving a each other, the resonance characteristics group are along the lines that we would anticipate from the earlier discussion of larger number of air molecules over the of the string are able to determine the shorter path. This is the equivalent, from period of time required for the bow to principles governing freely vibrating systems. We would expect the low-fre the point of view of power transferred l'egain its grip and to carry the string to the medium, to moving a smaller num on a forward journey once again. quency double bass, fo r example, to have strings of high mass and low stiffness ber of air molecules over a longer path, It can be readily seen that the vibra and results in the relatively strong and t ions induced in the string will not be of for its Helmholtz enclosure to have l arg~ deep fundamentals voiced by the bowed pure sine form; the stimulating force volume, and fOl' the sounding boards formed by the belly and back to be great or plucked double bass. The same princi * Contributing Ed-ito-I', AUDIO ENGINEER 111 area. The last expectation follows ples applied to speaker systems make pos ING. from the fact that the excursion of air sible the effici ent reproduction of bass. 36 AUDIO ·ENGINEERING • OCTOBER, 1952 Instruments of the bowed-string class of the lower notes are wrapped in order consists almost exclusively of harmon allow the performer to control timbre to secure the greater mass required by ics), while the hi gher notes contain a by different techniques of bowing which a low-frequency vibratory system. The progressively weaker harmonic struc def~r!n the string in different ways. In vibrations of the strings are coupled to ture. Like the violin, the piano may be addItIOn the. player, by changing the the air by a sounding board. plagued by a wolf note, which in this length of strIng left free to vibrate has The key mechanism of the piano case is more properly called a clang exa~t and continuous control of pitch. works as a. launching device. When a tone. The bass strmgs may form stand He IS able to use natural pitch intervals key is depressed the hammer is driven ing waves at relatively high frequencies and can apply frequency and amplitude towards the appropriate string, but is re (stimulated by the initial hammer im vibrato. leased from its driving mechanism, like pact) which are harmonically unrelated Pl ucked St rings a projectile for a sling, before the key to the fundamental. has reached its bed. The hammer is thus In contrast, the brass strikers of the The plucked string group includes the guitar, the harpsichord, and the harp. T he harpsichord is a keyboard instru ment similar to the modern piano but with a lever-actuated plectrum of le; ther fiber, or tortoise shell which pluck ~ rather than strikes the stt·ings. The harpsichord proper, also call ed the clavicem:balo, ordinarily has two man uals or keyboards. Occasionall y a third Fig. 5-2. Single piano ton e produced by a concert performer, compa re d to t he tone produced by keyboard and a pedal board are included. allowin g a weig ht to fall on the some key. (Courtesy J. Acous. Soc. Am.) Each manual has more than one set of strings, and each set of strings is con free at the point of striking, and it re- clavichord produce a tone which resem trolled individually by a stop, as on the bounds and reniains poi ed a short di s- bles that of the plucked harpsichord. The organ, so that the timbre of notes is tance from the string as long as the key cl avichord is a smaller instrument, some under the control of the player, who can is kept depressed. At the same time that times made as a table model, and does int~'od uc e or delete sets of resonating the string is struck its damper is I'e- not have as intense a sound as either the strIngs. In all models the coupling be moved. \iVhen the key is released the piano or the harpsichord. The striking tween the vibrating strings and the air hammer returns to its normal rest posi- of the strings of the clavi-chord is is a ided by a sounding board with which tion and the damper is again brought to achi eved with an entirely different me the strings are in contact, greatly in bear on the string. chanical system from that of the piano; creasing their effective area of radiation The piano tone may be controlled in a the brass tangent which strikes the surface. limited manner by pedals. These operate string simultaneously marks off the The harpsichord was the principal by adding or removing dampers, by re- length . of the vibrating section, and the 010 keyboard instrument, and held an ducing the length of the hammer stroke, key does not lose control of the string important place in the orchestra, until or by shifting the position of the ham- as it does in the piano. The player thus the cl ose of the 18th century. At that mers so that fewer strings are struck. "makes" his own notes, like a violinist time it was superseded by the piano. The mechanical system of a piano is or guitar player, and the introduction. Recently, however, there has been a re such that the player can exert no con- f r0111 the keyboard, of subtle variations birth of interest in this instrument trol over the acti on of the keys other of pitch and of vibrato are possible. which has ceased to be regarded as a~ than determining when, how hard, and old-fashioned piano and is accepted as for how long the key wi ll be depressed. Reedless Wind Instrum ents There is no such thing as artistic an instrument of unique quality in its The flute, piccolo, and pipe organ are own right. The timbre of the haJ'psi "touch" relative to a single note.! Figwre 5-2 illustrates the identity of tones pro the ma in instruments of this categol·Y. chord includes a much more extended The fi fe, fl ageolet, and recorder are range of higher-order harmonics than duced by a ~o n ce rt performer striking a key and by a weight falling on the same similar to the flute in that they make use that of the piano. of air-column resonance, while the The modern harp is a multistringed key. Descriptions of the quality of a piano performance which employ terms ocarina (sweet potato) and police instrument in which the strings are whistl e use enclosure resonators which plucked by hand, and in which the effec referring to the a rtist's "tone" or "touch" are not fallacious, however, be are of the Helmholtz type. tive length of each string can be short All of the instruments mentioned re ened in two semitone steps by a system cause the overall quality of the sound of a piano is formed by the -relationships, ceive theil' stimulating energy fr0111 a of pedals. Although the harp is one of steady stream of air. This stream is di the ~ost ancient of musical instruments, in intensity, timbre (as a functi on of in tensity), and duration, between the in rected against a hard lip, and eddies of havll1g been used by the EgyptI ans of whirling a ir currents are fo rmed, alter the 13th century B.C., the modern dividual notes. A particular performance may be thought of as having a "brittle" nately on each si de of the lip, as illus pedal version is less than 250 years old. tl'ated in Fig. 5-3. The effect is the same Its characteristic "ethereal" quality is or a "singing" tone, but these quali ties are not based upon the wave form pro as that of an actual reed vibrating back largely a function of the relatively small and forth ; for this reason these instru sounding board which forms its base. duced by the individual strings, which at a given intensity is unchangeable. ments are sometimes referred to as be The decreased area of the radiating sur longing to the air-reed class. face, compared to that of th e keyboard The vibrations of the piano string do not have a large content of hi gher-order The primary, non-sinusoidal oscill a striuge"d instruments, does not couple as tion thus produced is called the edge much a ir resistance back into the vibrat harmonics because of the nature of the hammer, which is felted and which has tone. By itself- the edge tone would have ing system; the amplitude of the tone is a natural fundamental frequency deter decreased, and the poor damping allows a rounded striking surface. The strings are thus not deformed to as angul ar a mined by the velocity of the ai r current the tone to persist for a longel' period in relation to the diameter of the edge, of time. shape, and do not produce a wave form with as much high-frequency content. but the primary vibratory system does St ruck Strings The richest timbres are in the bass (the not operate independently. It is strongly energy content of the very low notes influenced and al most controlled by the The piano and the clavichord are air resonator ·to which it is coupled, members of the group of stringed instru 1 The pianist can contribute a greater whose fundamental-harmonic resonances ments whi ch operate by a striking ac noise component to th e tone by a perCllssive force the hequency of vibration of the tion. The piano has more than one active stroke, and there is a trick, of no arti stic "air reed." The frequency of oscillation string for each key (except for the significance, in which partial damping is of the a il' column or cavity is also pulled lower bass notes) ; the five upper octaves attempted by momentary release and a use plain steel strings, while the strings second stroke. [C ontimted on page 88J AUDIO ENGINEERING • OCTOB ER, 1952 37 hew. 'lfMk'd. hewed S/vune to. -AuJ;.o.- Arrow's Audio Center Several innovations in demonstration methods and displays will attract many new comers to the ranks of Hi-Fi enthusiasts-and will please many an Old-Timer in the art. ETWEEN THE MANUFACTURER of au But the new Audio Center means As the customer enters the demon dio equipment and the ultimate just what the name implies-and Audio stration studio, he is faced with prac Buser is one important link-the job is certainly its central theme. The en tically every ampli fi er, speaker, tuner, ber. Here it is that the equipment is tire store-whi ch occupies the first and record player, and tape recorder on the shown a'nd demonstrated, pl'epared fOl' second floors of Arrow's fiv e-story market, all a rranged for ease of inter e a s y and efficient interconnection, building-is brand new from its new connection so that any combination of planned by the buyer and the salesman entrance and display windows to the equipment can be heard-just name it - who is generally somewhat of a hob back of the studio floor. Figure 1 shows and you can hear it. But the unique part byist himself if he is to be a success in the exterior, and F'ig. 2 shows the view of the demonstration floor is that there his work-and finally packaged in a which greets the customer as he walks are two-count 'em, two-studios, al manner which will fit into the precon into the building, Along the right is a most identical. Both are soundproof, ceived system which the user envisages. conventional counter which provides both are air conditioned (as is the en Here too is where the customer learns sales space for the smaller items, such tire store) , and both equipped with the the difference between pickups, record as pickups, replacement styli, recording same demonstration set-up. Thus it is changers, amplifiers, tuners, speakers, tape and wire, accessories, and similar possible for the customer to hear the and speaker enclosures. It is only by merchandise. At the rear can be found equipment in which he is interested careful inspection and aural comparison the "package" items, such as phono without interference from some other that many buyers can be satisfied. Such players, turntables, portable sets, P A customer-or, conversely, without in 'an institution is the new Audio Center equipment, and the lower priced tape terfering with some other customer. recently opened by Arrow Electronics and wire recorders. The staircase at the With audio becoming such an impor in the heart of New York's famous Ra left of the photo leads to the studio floor, tant part of everyday life, the traffic in dio Row-Cortlandt Street between one flight up, where most of the hi-fi most demonstration rooms is becoming Greenwich Street and the Hudson equipment is to be found. so great that it is almost impossible to River. Only two blocks long, this street enjoy a demonstration without at least has long been known as the center of The Studio Floor one "kibitzer." radio in Manhattan, even though sev The second floor consists of three Figu1-e 4 shows one of these demon eral other streets in the same vicinity rooms-two studios which a re essen stration-studios as seen from the foyer. have absorbed the overflow. tially identical, and the entrance foyer. At the back can be seen the "Merry-Go Many jobbers-or distributors, as This latter, shown in Fig. 3, provides Sound," a new idea developed by they are more properly known-have a comfortable waiting room so that Charles M. Ray, manager of the sound recognized the need for adequate facil each visitor may have the use of a stu division of Arrow Electronics, Inc. ities for the proper demonstration of dio all to himself, so to speak, duting This unit provides space for 24 diffe r audio equipment, but it remained for his demonstration. H ere, too, is a dis ent loudspeakers to permit comparative Arrow to open a second store devoted play of a typical system in a typical selection. These speakers are mounted entirely to audio. Their other store a living room environment-one which six on a side, and the entire unit ro block closer to the river handles capac might give the customer some ideas tates-controlled remotely from the itors, transformers, res istors, jacks, that he could incorporate into his own switching panel-to face six different switches, and the general run of radio home, unless he has planned his own speakers towa rd the li stener at a time, part store merchandise. system thoroughly in advance. thus making choice of speaker perform- Fig. 1 (below). Exterior of Arrow's new Audio Center, located in the heart of New York City's famed Radio Row at 65 Cortlandt Street. Two floors of Audio indicate that Audio has come of age. Fig . 2 (above). First floor showroom of the Audio Center, where the customer may buy a replacement stylus for his phonograph pickup-or a complete portable phonograph-or most any audio accessory. 38 AUDIO ENGINEERING • OCTOBER, 1952 rooID . • • there's no roo... for douLt There can be no room for doubt in the I continuity and fidelity of your broadcast. Precisely the reason you demancl-and get - the best in transmitting and studio equipment. Nor should you compromise with quality in the tape recorder you select. . In AMPEX Recorders you will find the same matchless reliability and performance you expect of your transmission equipment ... and for the same reason - they are engi neered to the highest professional standards. AMPEX hrings you these cost· saving operating advantages: • UNINTERRUPTED SERVICE Under the demand of heavy-duty programming, AMPEX Re corders deliver thousands of hours of unbroken service. Recently a set of AMPEX heads was returned from Honolulu for routine replacement after 11,000 hours continuous use, 17 hours a day. The heads were still within AMPEX specifications for new heads and had several thousand more hours of use remaining. • ~IINIIUUIU ""DOWN TI~IE " AMPEX Recorders are designed for thousands of hours of con timious operation with minimum "down time," resuiting in low , maintenance costs and protection from sudden broadcast failures. • ACCURATE TIMING AMPEX split-second timing accuracy protects your programs and commercials from embarrassing time overlaps. • HIGHEST FIDELITY Even when programs are repeatedly transcribed from one tape to another, there is no noticeable build-up of noise level, "wow" or distortion. • LONG LIFE AMPEX Recorders are designed and built for years of service dependability. Its recordings match established NARTB stand ards. When you have an AMPEX, you have a machine built for years-ahead performance. IF YOU PLAN FOR TOMORROW, BUY AN AMPEX TODAY FIEX MAGNETIC RECORDERS AMPEX ELECTRIC CORPORATION 934 CHARTER STREET • REDWOOD CITY, CALIF. AUDIO ENGINEERING • OCTOBER, 1952 41 But, unfortunately,. one stairway led Only at-the-moment voice instructions serve day-in-and-day-out the purpose of directly into the blazing fire area on a can assure this being done. an ordinary sound system, as an effi lower floor, and many of the children 3. Direct people, including uIldrilled visi ciency tool of limitless application in tors, to different safety shelters; and then were trapped. It was not possible to routine industrial and commer cial op possibly re-direct . them, later, to other er~tions. modify the pre-defined alarm signal to shelters because of the development of direct the entire ·floor to use the safe close-by danger. Simple signals could stairway. never do this. Design Needs There is also the uncontrollable psy 4. Caution employees and the public to The requirements of a S~rviva l Sound chological reaction of undrilled people move in an orderly manner to thei r System a re much more demanding than to the wail of the siren, the clang of the designated shelters so as to restrain hys those of an ordinary sound system. Its alarm bell, and the startling staccato of teria or stampede. Recently there has serious purpose allows little leeway for been released a 16-mm film entitled "Tar compromises in performance or price. frenzied whistle blasts when these signal get U.S.A." des ig·ned to instruct plant devices are restricted to emergency employees how to act under conditions The audio engineer planning such a sys warnings. In American life these sounds of an enemy air attack. The film portrays tem should bear the following uppermost mean danger. Coming with sudden un the sounding of the air raid alarm arid in mind: expectedness, they shock the heart with the wild rush to designated shelters. It apprehension. The first r eaction is to shows developing panic as people madly 1. Major emphasis on speech intelligi drop everything atld run- unorganized scramble through bottle-neck doors and bility. Particular instructions may be - anywhere. Even when their use is corridors, but only the commentator in issued only once; 20 per cent of the per restricted to disaster signals, and all are the film is able to caution the rushing sonnel may be hard of hearing, but mob to "take it easy." H ow simple it every syllable must be instantly under well-informed of their meaning, they would be if the Defense Coordinator, stood as it may mean life or death. It breed fright and terror, particularly with the facilities of a Voice Sound Sys cannot be chanced that anyone will mis where masses in enclpsed areas are in tem, could do this very thing. understand instructions and run directly volved. Nothing can be more serious in S. It will be easier to confini people in into the arms of disaster instead of factories, office buildings, apartment shelters for a prolonged time if the De running the other way. The best quality houses, and other structures housing fense Coordinator can cut in on shelter of equipment only will suffice-quality many persons and having a limited loudspeakers periodically and reassure as relates to reliability as well as repro number of elevators and exits. the occupants. If "this is not done, un duction. No junk, typical of many sys certainty may breed panic. The situation tems for paging or music distribution use The great uncorrectable weakness of is no different than that on a man-o'-war where it matters little if listeners under these signals lies in the uncertainty in battle, when the battle announce system stand only SO or 60 per cent of the which follows their use and their in is used every few minutes to acquaint words pronounced. ability to follow through with detail in those below deck how the fight is going. 2. Loudspeakers mtist be installed liber structions that everyone can understand Knowledge that the rocking blast on the ally, with horn types used in locations of and follow with confidence. This weak port side was close but not damaging high noise level. In addition to usual ness, more than any other, is making makes it a hundred times easier to stick locations, speakers must also be installed coded signals unacceptable in the new to their posts. in toil ets, washrooms, warehouses, load 6. Call rescue workers fr0111 one part of ing platforms, corridors, elevators, base tense Defense El-a that has been ushered the premises to another to administer to ment storage areas, and parking lots. in by the Atomic Age. first-aid cases res ulting from either at 3. Switching provisions should be pro tack or hy steria. The need for more vided so that loudspeakers can be con The Logical Solution stretchers or more smelling salts can be trolled by zones. It should be possible To survive in this new era, we are communicated only by spoken directions. to talk to people confined in shelters 7. Direct trained and equipped crews separate from plant-wide direction of going to have to rely upon many coordi direct to points of need, such as to turn emergency crews. Likewise, if the De nated precautions. There seems to be off broken water, chemical, or electrical fense Coordinating Dispatcher knows only one way to achieve this v ital co mains or to prevent other equipment that the first-aid crew is operating in ordination at the civilian level-local hazards that might develop while un Zone A, it should be unnecessary to call communication networks of loudspeak supervised. to all other zones to re-direct the crew ing electronic systems that can sound the 8. Instruct the Wardens to vary ventilat to a need in another location. standard alert signals and then follow ing controls throughout the premises in 4. Since many of the above speaker loca through with detailed spoken instruc the case of radiological, chemical, or bio tions wTH not be utilized in routine day tions which will calm human fears and logical attack, or to provide isolation to-day use of the sound systems, priority of highly combustible materials in case circuits must be provided whereby all direct orderly teamwork under any emer of fire or explosive attacks. speakers can be actuated and any special gency situation. 9. Route de-contamination crews from speech equalization cut in, in cases of Consider the many situations which poi nt to point to clean up hazardous con emergency. may have to be dealt with in a medium ditions and report on their safety. S. Microph one inputs must be provided siz·ed plant or office building in case of 10. And last, to call on wardens and at the Building Defense Control Center, enemy air attack, and how a Voice emergency crews to report back and as plus inputs on each separate floor and in Sound System throughout the premises sure that safety exists before the All each building, as well as in important Clear signal is sounded and employees areas of large enclosures from which it would be the D efense Coordinating or public are allowed to return to their might conceivably be desirable to direct Officer's most valuable tool for mini normal activities. defense activities. mizing danger to human· lives a nd com 6. Consideration should be given to pro pany property_ Sirens, whistles, horns, bells, gongs viding emergency speaker circuits fo r Here are some of the directions the and buzzers-even when ably supple carrying on, should one of the main cir Defense Coordinator-acting as a mas mented by telephone and message run cuits be damaged. This might be ac ners-cannot do this man-sized job. ter dispatcher- must get over quickly, complished by wiring all circuits as loops They are as puny as voice tubes. so that input can be prov ided from either clearly, and in a manner to inspire con end. fidence: Up-to-Date Requirements 7. An auxiliary power supply must be provided for use should the standard L Sound the standard alert signal to gain A loudspeaking electronic system ca- . power mains become inoperative. Gas attention. Then follow through with a pable of transmitting the standard driven generators appear most appro vocal explanation to assure that every Alerts, plus Voice and Music, is required priate. The size of auxiliary power plant one, including visitors, understands the in every good-sized building to discharge to operate a Survival Sound System will significance of the signal. By being able the safety responsibilities of this new often be only a fraction of the size of to give a spoken explanation, it is less Atomic Age. Sound Systems designed power plant that would be required to necessary for drills on costly company operate other types of signaling systems. time. to perform tllis special service have been dubbed " Survival Sound Systems"-not 2. Call upon workers to shut down their Modifying Present Systems machines, unplug soldering irons, turn off a warning system, not a disaster system, chemical processes, and so on, before but a system designed for Survival. Existing sound systems can profitably leaving their posts, to prevent possible In addition to being built to life-saving be r esurveyed and brought up-to-date to fires or other damage ·while unattended. specifications, such a system also can meet these Survival System standards. 42 AUDIO ENGI NEERI NG • OCTOB ER, 1952 how is the • In plug-in audio amplifiers II • - only 2 of standard panel space IF you use the, NEW Langevin 5000 Series TYPE 5116 AMPLIFIER A plug-in, low-noise pre-amplifier for use in broadcast audio facilities, recording, or sound systems. ·Can be used as a booster amplifier with + 18 dbm output. Gain: 45 db into unloaded input transformer, with provision for adjusting to 40 db. Input source impedance: 30/1;;0/600 ohms_ Center tap available when strapped for 150 or 600 ohms. Output load impedance: 150/ 600 ohms, with center tap on 600 ohm position. Output noise: equivalent to input signal of -120 dbm or less. Output power: +18 dbm (0.163 watt) with less tha,n 0.5% RMS total distortion from 50 to 15,000 cps, only 1 % at 30 cps_ TYPE 5116 AMPLIFIER Frequency characteristic: ±0.5 db from 30 to 15,000 cps. '. 11 will fit across standard rack • Power requirements: 6 rna DC at 275 v, 0.3 amp at 6.3 v. Tube complement: two Type 5879_ TYPE 5117 AMPLIFIER A plug-in, low-noise, low-distortion, fixed-gain unit for use as a program monitor or booster amplifier in broadcast audio fa cilities, TYPE 5117 AMPLIFIER reco rding, or sound systems_ • 6 will fit across standard rack Gain: 55 db, fixed_ Input source impedance: 150/600 ohms, center tapped_ Output load impedance: 150/ 600 ohms, with center tap on 600 ohm position_ Output noise: equivalent to input signal of - llO dbm or less. , Output power: + 30 dbm (l watt) with less than 0.5% RMS total distortion from 30 to 15,000 cps; 39 dbm (8 wattsi with less than 1 % RMS total distortion from 50 to 15,000 cps. Frequency characteristic: ± 0.5 db from 30 to 15,000 cps. Power requirements: 70 ma DC at 300 v, 1.2 amps at 6.3 v. Tube complement: two'Type 6V6, two Type 5879_ TYPE 5206 POWER SUPPLY A plug-in unit capable of powering as many as 22 Type 5116 pre-amplifiers, or 10 Type 5116 pre-amplifiers plus two Type 5117 monitor amplifiers. Load current: 210 .ma DC at 300 volts, Filament current: 6.5 amps AC at 6.3 volts. Ripple: less than 2 millivolts pre-amplifier supply, less than 10 millivolts monitor amplifier supply. Power requirements: 105-125/210-250 volts, at 50 to 60 cps. Redifier: t~o type 5Z4 tubes. TOGETHER FOR THE FIRST TIME! Compactness beyond belief • Top broadcast quality • Balanced output • Low-impedance input. Plug-in construction. Gold-plated plugs. Only 3 tube types. Tube-pull without plug-out -. Plate-current-check switches. I LENGTH , 9V." 3 WIDTH , 7 /,'" Why not try Langevin for your transformers - custom-built .to [,:' HEIGHT , . 3V1" 1 WEIG/iT-, ),7 .lb •. 6 oz. TYPE 5206 POWER SUPPLY commercial or MIL-T-27 specs. Fastest delivery in the country on L. ,- -:., .... • 2 will fit across standard rack. test samples! ~ SEE US IN ROOM 531 AT THE 1952 AUDIO FAIR ~ means the linest in audio components. • amplifiers. LANGEVIN MANUFACTURING CORPORATION Iransfarmers • power supplies 37 WEST 65TH STREET NEW YORK 23, N.Y. AUDIO ENGINEERING · . OCrOBER, 1952 43 Nuclei now exist in many forms which ard alert signals, even through the can be built up readily to provide Sur heaviest traffic noises, and should under vival Sound System service. For in standing of subsequent voice instructions stance, the addition of microphones, plus be difficult, people could quickly ap loudspeakers in shelters and other work proach the nearest speaker, which never ing areas of existing wired-music sys would be furtl'ler away than a fe'.'1 hun tems in restaurants, hotels, and offices dred feet. If efficient speakers are used, would convert these to valuable warning a centrally located, remotely controlled and direction systems. The same applies l-kw amplifier could feed speakers to the already existing high-quality enough to checker-board an area of 100 sound systems in motion picture theatt·es. street intersections. This would be suf CALIFORNIA T he trend towards di scarding simple fici ent to cover the business sections of Burbank : Va lley Electronic Supply Co. most cities, and the number of units re HoIIY-Nood: Hollywood Electronics signals within buildings is only part of Long Beach: Fred S . Dean Co . quired for the largest cities would be Los Angeles: the "No Coded Signals" story. The same Calif. Rad io & Electronics CO. within reason. I nternational Radio & Television P arts CO. arguments that favor loudspeaking elec Radio Products Sales, Inc. tronic systems within enclosures apply Radio R ecorders Equipment Co. Unirersale Radio Supply Co . with equal force to outdoor warning sys High-Level Systems Oakland: W. D. Brill, Co. tems fo r general public use. E lectric S upply Co. So much fo r low level systems. It is Millers Radio & Telcvision Supply "Siren, whistle, and horn air-raid warn E . C. Wenger, Co. the hi g h level system consisting of a Pasadena: Dow Radio, Inc. ings only alarm, confuse, and incite few high power loudspeaking units at San Franci sco: panic. Their weakness lies in the un Ets-Hokin & Galvan widely spaced locations that seems to Hal Cox Co. certainty which follows their initial San Francisco Radio & Supply Co. have the most glamour appeal to muni Tele\'islon Radio Supply Co . sounding. T hey cannot fo ll ow through Wholesale Radio & Electric Supply CO . cipal authorities, possibly because it CONNECTICUT with explicit instructions; they cannot mimics the existing siren practice. New London : Aildns Electronic SUDPlies, Inc. reassure; they cannot tell the populace DELAWARE Wilmington : what to do should an unanticipated e m ~ r The hi gh level system poses two big A IIno Radio Co . engineering questions: First. can it COIP Radio E lect.r ic Scn'ice Co. of Penna. gency occur requiring action other than FLORIDA that for which people have been drilled. municate intelligible speech reliably over Pensaco la : Grice Radio & Electronic Supplies appreciable outdoor areas, even in resi ILLINOIS T hese systems are costly to install, and, Chicago: dential sections? And second, can exist Allied Radio Corporation being mechanical, are relatively trouble Newari{ E lectric Company some and unreli able. To provide them ing electronic equipment economicall y IOWA reproduce the required acoustic levels? Des Moines: Radio Trade Supply CO. with an emergency power supply is im MARYLAND There seems to be a plausible answer Baltimore: Wholesale Radio Parts Co., Inc. practic~b le. MASSACH USETTS Many Civil Defense officials a re di s to the first question. It is proposed that Boston: Hatry & Yo ung satisfied with the siren, even as an alat"m intelligence should be possible under ad Radio Wire Television Inc. The Radio S hack Corp. device because of the possibility of COIl verse conditions if the message is limited Springfield: Regent Sules Inc. to phrases of only two or three words, MICHIGAN fusing siren-generated Attack Warning Detroit : K .L.A. Laboratories, Inc. Signals with other established emer and these discreet phrases repeated over MISSOURI and over many times. For instance it Kansas City: Burstein-Applebee Comp any gency services. S irens have been used NEW HAMPSHIRE for years by police, ambulances, volun mi ght be desirable to follow the s tan d~rd Concord : Evans Radio warning signal with information to pre Manch ester: Radio S ervice Laboratory teer fire departments, and penal institu NEW JERSEY tions. S ince all sil"ens sound substanti"ally pare for a fire bomb attack. The word Atlantic City: Alm o Radio Co. Camden: Alma Radio Co. the same, disastrous mis-cues are pos "fi re" could be repeated over and over Newark: Aaron Lippman & Co. sible. again many times. It it should be expedi Emerson-New J ersey. Inc. ent to in struct the populace of an entire Radio Wire Television, Inc. An all-electronic public Warning Red Bank: Monmouth Radio SUDPly CO. System could easily sound an endless area to evacuate in a certain di l"ection, NEW YORK the words "Go North" could be repeated Albany: Ft. Ora nge Radio D istr. Co . variety of distinctive non-confusing sig Brooklyn : over and over again until it was rea Acme E lectronIcs nals and at the same time offer the an Benray Electronics Cor p. sonably certain that all people outdoors Electronic Equipment Co. , Inc. swer to other deficiencies of the siren. Hemllstead: understood. Davis E lectronics Corp. However, it appears unlikely that en Hicksvill e: Gem Electronics Distributors. Inc. tirely practical electronic systems can be The second question, of whether pres Jamaica: Peerless Radio D i stributors, Inc. New York City: offered until engineering study resolves ent-day electronic systems can put out . Arrow Electronics, Inc. Bruno, New Yorl;: some of the wen-known' vagaries of adequate acoustic power, is another mat ConsoHdated Radio Sales Corp. ter, particularly in view of the fact that E. W. Associates, Inc. transmitting sound and intelligible F ederated P urchasers speech over large outdoor areas. Civil Defense officials are continually Harrison Radio Harvey Radio Under conditions of good transmis crying for louder and louder signals. It Hudson Radio & TV Co rp . appears probable that electronic systems Leonard Radio, Inc. sion, outdoor sound can be heard many O. & W . Radio Co. miles, while under other normally-to-be can be put together with presently avail Radio Wire and Television. Inc. able eq uipment which will provide as ~~~lm~~~iOR~di~I<:5~~~I~iCS Co. expected weather conditions the I"ange Rochester: Roc hester Radio Supply Co. of the same sound may be reduced to a strong a signal as a 2- or possibly S-h.p. White Plains: Hi Fidelity Center electric siren, although at an unfavorable NORTH CAROLINA fraction of a mile. Building obstructions Raleigh : Southeastern Radio Supply CO. cause garbling due to reflections and cost ratio of two or three to one. Such OHIO systems might have a reasonably reliable Akron: Olso n Radio Warehouse, Inc. dead areas due to acoustic shadows. In Cincinnati : Steinberg's, ·Inc. radius of a quarter or maybe half a mile. Cleveland ; The Progress Radio Supply CO. concentrate4 areas of people and traffic OREGON activity, the ambient noise which must Electronic systems to compete with high Portland: Hawthorne Electronics pressure air h01"nS, high pressure steam PENNSYLVANIA be pi erced is hig h and variable. These Allentown : Norman D. Steed Ie Co. sirens, and high horsepower gasoline Easto n: Radio E lectric Service Co. of Penna. adverse factors are most troublesome in Philadelphia: congested downtown business areas driven air sirens are entirely out of the Almo Radio Co . question. Radio E lectric S ervice Co. of Penna . where buildings are tall, streets narrow Scranton : General Radio & Refrigeration Co. and canyon-like, and traffic heavy. Scranton Radio & Television Co . Wilkes ~ Barrc : General Radio & Electronic Co. It seems probable that 'such business Conclusions York: York R adio & Refrigeration Parts a r ea~ RHODE ISLAND can be covered reliabl y only by In closing, It IS important to reiterate Providence: relattvely low-level systems consisting Wm. Dandreta & Co. the seriousness of our immediate Na W. H. Edwards Co ., Inc. of many loudspeakers at frequent loca ti.onal Defense task and to cite two spe TEXAS tions. Two low-power hem-type speak Dallas: A lI ~S tat e Distributing CO. Cl (iC examples where audio can make Ft. Worth: Fort Wort.h Television Service ers pointing in opposite directions at important contributions. . WASHINGTON each street intersection could do the job Seattle: SeatLlc Radio S upply. Inc. WASHINGTON, D. C. of blanking each block with the stand- [Co11tinll ed on page 69] Electronic Wholesalers Inc. 44 / AUDIO ENGINEERING • OCTOBER, 1952 -. · .. world renowned for 33 iyears as the last word in precision 'electronics ... PILOT .• '. favored communications equipment of engineers, naviga tors; experts in the field ... [PILOT now puts its wealth of know-how into the most brilliant ,FM-AM Tuner ever built! Noth ing has been spared to 1TIake the ilew PILOTUNER truly the ulti T[!aie among Hi-Fi Tuners. Space permits li sting only a few of the many ,outstanding specifications, which include: ;1two stage audio a~plifier with bass and treble control ;units • two stage preamplifier properly equalized for 'use with variable reluctance cartridges, · RF stage for improved sensitivi ty and selectivity • automatic $ 95 fu~~ ,~!:cy contr?!. A remaTk ~b l e value at . .. 99 #t£~ PIlOTONE Amplifier #t£~ PILOTONE Pre-Amplifier Model AA-901 Model PA-911 Superb new amplifier with full Williamso n circuit. Constructed in accord A companion unit for PILOTONE AMPLI~ ' ance with rigid Pilot specifications. Contains 4 amplifier tubes, FIER Model AA 901. Selector switch allows quick choice of 1 rectifier tube. Power output, 10 watts. Total harmonic distortion, Auxiliary, TV, Radio or Phono inputs. Three positions of switch less than .1% at 10 watts output. Sensitivity, 1.5 volts RMS input for phono input give proper compensation for records made to for rated output; input resistance 470,000 ohms. Speaker output, AES, NAB and foreign standards. Seven input jacks on back S' and ,16 ohms. Front Pilot light ; on-and·off switch. Hum and permit quick connection of various types of signal. Separate noise level 80 db. below full rated output. KT 66 English Tubes. microphone input channel permits voice to be superim posed on, Dimensions: 14'" wide; 7" deep; 7Vz" high. radio, TV or phonograph. 12" long x 5Vz" x 5Vz". A luxury instrument, priced at $99.50 An exceptional "buy" at $29.95 The Pilot High Fidelity line is discussed and appraised in the prac tical new book, "High Fidelity Simplified," by" Harold W. Weiler Write for circular AE-J describing these superb PILOT High Fidelity Instruments in complete detail. PILOTRADIO CORPOR;fTION, 37·06 36th St" Long Island City, New York AUDIO ENGINEERING • 'OCTOBER, 1952 45 speakers, the RJ bookshelf model and the T he RJ 8-inch bass on many works with Bass-Shy EW modified bass reAex ( 16" x 11" x 14" ), big bottom, notably organ music, heavy Ass AND M ORE BASS. The trend towards my conclusions are not quite what might be brass and kettled rums and the like, is hard highs and more highs, which eventually expected. I'm getting bass-shy. to believe. (Give W harfedale credit too.) A Bwent supersonic and so reached a sensation. The RJ's bass is relatively so relative equilibrium, is now replaced by the huge that a really high powered high r ange rush to the lower regions-along ,with the is necessary fo r ideal tonal balance. This happy interest in small enclosures that Ba la nce little RJ is up in the former area of the 15- began a year or so back. The most obvious necessity, when it inch speaker, where a tweeter was de H ow much bass do we want for home comes to big bass, is balance-an equivalent rigeu.r. On the other hand, the E Vv, with music ? Let me say, in a few words, that range and fo rce of highs. T he musical ear somewhat less bass and a shade more in the I'm rapidly beginning to think we don't is far more sensitive to an imbalance of highs, is perfectly balanced for music. H ere want "all" of it. I'm not speaking particu highs and lows, about a central pitch, than we run into a whole new set of balance larly of those last few bottom cycles, which it is to any lack of either. Cut off the highs problems, created by the new ar eas of bass like the ultra-top ones are not realIy of and lows both, and you have the average rep roduction now available. much importance in actual music (witness small phonograph or radi o which pleases the diffi culty of finding a "good 30-cycle millions musicall y, and with good solid rea bass" recording). I mean the really impor son. Add more highs, you need more bass, tant bass, below that available in most good and vice versa. Boom bass reflex enclosures and above too, the The RJ, 8-inch, as elsewhere described in whole lower area, "'flat," relatively, instead this column, adds a lot more bass. My ear But there is more to this than balance. of peaked. quickly tell s me without measurement that Big bass is extremely touchy in a.!~y r OOIl-l No question about the desirability of non this small box gives me more of the stuff which is SIn.a ller than th at in which the orig peaked bass. Resonances, peaks of any old than myoid IS-inch bass reAex set-up ! inal ln1tsic might have been played, due to sort, make for distortion. Musical distortion. But, in this case, though the W harfedale standing waves and other multiplying an Just as bad, humpy bass leads to rumble and speaker has the highs to match, there is a noyances. boom from turntable motors. The best sign very slight attenuation. due to the RJ It is musically ri sky, I feel, to introduce I know of true bass response is (a) un principle itself. Very slight, I emphasize, on really low bass into any small room or even usually low rumble and bumble along with direct comparison ;with the same speaker in into a medium-large room of the usual home the big Io.w notes and (b) similarly, a very the EW direct radiator. sort. It may be fin e. But then again, it may natural, unboomy reproduction of the speak The EW enclosure (with in ternal baffl es not at all. Strange and disturbing booms, ing voice. P eaked bass, it la jukebox, brings that lengthen the path and remove parallels) shakings, peaks are more than likely and, out rumble and makes a travesty of the gets extraordinary bass fo r its size, far though a technician may overlook them, voice. more than most large home consoles and as most musical people will be decidedly an No ques tion, either, that from an engi much as larger 12 inch bass reAexes; but noyed. N othing is more distracting than a neering viewpoint we must strive towards not as full or as low a bass as the RJ 8- persistent resonance in the bass-and it's a the nearest thing to perfectly " Aat" bass re incher. lot worse in the room than in any cabin et; pI;oduction that ingenuity can devise. H ow do these two compare in a home AB your ears are right in the middle of it. But music li stening, especially in the listening test. RJ suffered from this at last fall's A udio average smallish room is, I'm increasingly F irst let me throw out a much-needed Fair in the con fi ned space of a hotel room. convinced quite another matter. N ine tenths scale of values here. W ith the W harfedale In my large summer cottage room. two of our listening is essentially artifical ; we or PermoAux, or un doubtedly with other stories high with a balcony opening off and have no literal reproduction, quite asi de new 8-inch speakers such as the University a peaked cei ling- not the sort of room from the vital absence of the binaural. We Diffusicone, both these boxes give a quality you'd expect to cause trouble-the RJ 8- reproduce, from a single point, sounds that and fullness of musical sound that is abso inch nevertheless set off some noticeable and not only were "wide" in the original but lutely amazing to any person not conversant di stractin g low-bass booms on piano and are .intended for much larger rooms, hall s. with super hi-fi equi pment in the large. other records. I am qui te certai n they were at greater distances. W e project the record F ar better than the fanciest standard home in the room itself. Moving the speaker ing hall liveness into our own rooms fo r a machine I've ever heard. Easily eq ual to the changed them. The EW enclosure, with less double liveness effect. Altogether, a sound of many a larger hi-fi system of past low bass, stirred the same booms up, but to thoroughly garbled reproduction, from any years. Volume enough fo r 95% of musical a definitely lesser extent and with less con literal point of view! But we are not out to people, listening in homes. D istortion low cious annoyance in the listening. be literal. luckily. enough to all ow for hours of unfatigued The low-bass enclosure, in one or another And SOl .with my first good try at two of li stening. As representati ves of the new of its fo rms. expensive or budget-pI'iced. is the new mexpensive enclosures for 8-inch trend, both these boxes (I have unfinished bound to incur a rash of criticism on this models, bottom priced) rate very high in score in the coming months, as the cus * 279 W. 4th' St., New Yo·rk 14, N. Y. the scale of musical value. tomers tryout the bottom cycles in their 46 AUDIO ENGINEERING • OCTOBER , 1952 / THE For it is a fact, that of the thousands of MOST AUDAX users, more than 70% bought the AUDAX POLYPHASE-even though they already owned other makes of pick.ups. The revolutionary new records are so true to the original that almost any pick.up is bound to give some results . . . but-it WANTED takes a reproducer of the highest order, one sensitized to the nth degree . . . a CHROMATIC POLYPHASE-to bring out every subtle shading, every nuance so es· sential to the real music of which these REPRODUCER discs are capable. Available to fi t the new compass·pivoted A UDAX arms and to fit record changers. Never before such LISTENING.QUALITY, such FAITHFUL REPRODUCTION but YOU and only YOU can decide what sounds best and most pleasing. Therefore ... SEE and HEAR POLYPHASE and YOU be the judge, One single magnetic unit plays all home records- replaceable Sapphire or Diamond styli. Be sure to obtain a copy of 1953 ELECTRONIC PHONO FACTS from your distributor. AUD1~K COMPANY 500 Fifth Avenue New York 36 Creators 0/ Fine Audio-Electronic apparatus jor over 2S years. I "C]I (?t I I I) J II,-c I , .Are 0udaed and Va fu.ed" J he ~I a nd arc! by VVh" h Q"l . h er~ C7i II small rooms. How much of it will be mis nata (above) . Goldsand finds Schubert n ot quite directed to the enclosure, when the room is big enough sounding, brings out the bigger mo· ments, emphasizes the larger Romantic mood, of the cause? Musically you cannot pit low which Schubert was a great pioneer. B-S brings bass resonances against not-50-low bass that out the equall y important delicacy, the classic is both balanced and unresonant. The musi directness and simplicity of Scbubert. Two very cian ;will pick the latter every time. different interpretations-but both highly musical Maybe what we need is a variable bass and decidedly valid, cut-off in our amplifiers! The B·S Mozart sonatas, emphasizing the piano, are tops in that instrument; Barylli's v i The post office is not geared to summer olin is sweetly but not very forcefully expressive_ travel and this department, operating re (Try the old Krauss·Goldberg versions, D ecca mote-control from the country, r eceives a LP reissue, for top Mozart fare.) The fami liar strange collection of those records which Beethoven Concerto is unexpectedly fine in this manage to survive the forwarding process Scherchen-B·S collaboration; perhaps it is B·S r efl ecting the persistence of the more enter who gives it a s implicity, a casua lness, that is prising sales offices who will not accept too much lacking in the self-consciously noisy performan ces we al'e used to_ Few performers AUDIO shipping defeat ! Musically unrepresentative, can do Beethoven without being stage-struck, but interesting just the same. By next like every actor when he gets to "to be or not month, no doubt, the fall flooding of discs to be!" ATTENUATOR will be digested to the point of description R ecording? By Westminster-enough , now, to in this space-it takes time to listen. (And insure high quality. The solo B·S piano is a bit plenty of record dealers won't be getting bass-heavy; I suspect a mike som ewhere under the stuff in stock until months after the an neath the sounding board. But the top is liquid and natural, no false percussions. 'I'he sonata nouncements. Just like audio equipment!) puts the viGlin ratber s urprisingly in the back· H ere's what's new at the moment. ground, the opposite fault usually being th e case. T he concerto is beyond criticism. Bach, the Arranger Goldsand Bach, Brandenburg Concertos #2 and # 4. London Baroque Ensemble, Karl Haas. Matched! Schubert, Sonata in A, Op. 120; Moments Westminster WL 5113 Musicaux, op. 94. Robert Goldsand, piano. Bach, Keyboard Concertos ( Harpsichord) Concert Hall CHS 1148 # 3 and #6. Maria van der Lyck, hps. ; Schubert, Impromptus, Op. '142. Goldsand. Ton-Studio Orch., Michael. Concert Hall CHS 1146 Period SPLP 547 Brahms, Variations on a Theme of Paganini, B ach 's keyboard concerto #6 in F win amaze Books 1 & 2, op. 35. Goldsand. many Bach listeners-for it is the 4th Branden Concert Hall CHS 1147 burg, fOl- two recorders, in a Bach arrangement, Lis:z:t. Six Crandes Etudes after Paganini. designed for his own us~ . T h,e original was for Rachmaninoff, Variations on a Theme of two recorders and violin, in G; the arrangement Chopin, op. 22. Goldsa nd. substitutes the harpsichord for the fiddle, F for G, and Bach revamped much of the detail to al· Concert Hall CHS 1149 low the keyboardist (bimself) to shine. If you An unusual piano series, matching the m an to think that the modern arranger is a m ere skilled the m usic- as the large companies often fail to technician, you a r e right; Bach combined skilled do. Goldsand is a fiery Romantic in the old arranging with skilled composing, an,l did both sense; no apologies, no streamlinings-he takes almost day by day. the old boys' hair-in-the-eyes stuff as it was in The two Westminster discs are brought to tended, plays it to the hilt. It's remarkable how gether and re... cut from earlier sides on two dif fine the Romantic outbursts sound when they come ferent records. The Period is part of the r ecent througb full power! A sensitive musician and a Stuttgart Ton-Studio set'ies of Bach and Mozart. terrific technician, Goldsand is ideal for the big. Both use the correct- and colorful- original in gest, loudest piano music of this type. s truments, recorders instead of flutes. harpsi Liszt. Brahms, Rachmaninoff are his best m eat chord instead of piano. Gorgeous recording and -full blown piano. His Schubert is lovely- bring· perfect for hi-Ii reproduction. Of the two, the ing out the more Romantic side, both the weighty P eriod is the heavier and m ore solid. a bit plod p'auses, the pregnant key-changes, and the stormy ding, the vVestminster players are light-footed. passages. Goldsand makes the most of the impres' sive but not overly profound Liszt and the gloomy Hi-Fi Froth Rachmaninoff variations, (on an ultra-familiar Chopin theme)- to please tbe touchy hi·fi fan. There's plenty of easy hi·fi listening for those as The Brahms and Schumann disc offers weightier wants it, especially in the newly popular short Single & Dual fare, the Brahms a famous pianist's virtuoso piece LP lO-inchers at lower prices-just possibly in potentiometers here played effortlessly, the Schumann a tremen tended to m eet Remington and similar competi V. U. meter multipliers dous and lengthy early work, hard to pulJ t o tion. Decca's 4000s and Columbia's AAL series gether into coherence, and beautifully flowing in are t ypical. Multi-impedance matching aHenua.ors Goldsand's understanding interpretation. \ Excellent piano recordi.ng, a bit on the hard side Fixed attenuators Operatic Arias played by Camarata and His \ with a few touches of false transient sound in the Orch. (No voices!) Decca D'L 4008 louder tones, a bit of waver here and there. Big, Romantic Reveries (organ). Vi rgi I Fox. natural sound more than makes up for it. Shallcross offers a complete Columbia AAL 1 8 line of over 200 standard fixed, Dinner Music-Sigmund Romberg & His rotary-step, and key type atten Orch. RCA Victor 9019 uators to match practically any Badura-Skoda Three schmaltzy representatives of good re· audio requirement. Complete cording- vocal arias without the voices (but with facilities are also avail'able for Schubert, Eight Impromptus, op. 90-142. all the juice retained and sugar added), war·horse making custom-built units to Sonata in A, op. 120. Paul Badura-Skoda, reveries for the biggest of organs-both the wed. specifications. pf. Westminster WAL 205 (2) ding m arches, and more of the sam e-and, for Mozart, Violin and Piano Sonatas, K. 377, those who like it (ugh-pardon m e) , the Best of K. 305, K. 58. Badura-Skoda and Walter Romberg with a huge, semi-jazz pops orch. '\Von Barylli , VI. Westminster WL 5145 derful collection of hi·fi stuff. Beethoven, Piano Concerto #4. Badura Concert Souvenirs. (violin and pi ano) . Louis Skoda; Vie n n a State Opera Orch. Kaufman, Paul Ulanowski. Scherchen. Westminster WL 5143 Capitol L-8165 Another pianist of outstanding ability in the Encores by Zino Francescatti. with Artur musical way, here featllreg in several continuing Sha II cross Balsam, pf. Columbia ML 4534 series, including his own soio work. As Goldsand centers best upon the middle to late fiery R oman The inevitable old favorites of the violinist's MANUF.I{CTURING .COMPANY tics, B-S fits beautifully at an earlier focus, his after-concert repertory. L ondonderry A ir, etc. best work being Mozart, to my ear, and Schu Francescatti m aintains the better dignity; Kauf bert, tb'e early Romantic. The two m en overlap man oils his to the dripping point. Both are good Collingdale, Penna. very interestingly in the Schubert A major so· in sound, the Kaufman closer, sharper. 48 AUDIO ENGINEERING • OCTOBER, 1952 Some Pickup Design Con'siderations P. G. A. H. VOIGT:: A discussion of one of t he causes of unequal wear on the two sides of a stylus-and a suggested cure ,for it-by a writer who has buil t and so ld pickups commercially over a long period. N THE AUGUST (1951) issue, Mr. Ginn asks if anyone else has ever B I put a spring on a pickup arm to counter the unwanted force which acts toward the center of the record when offset heads are used, claiming that such a spl-ing improves mattel-S. He and other JE readers may be in terested to learn that in the pre-war German T elefunken pickup, a spring was fitted into the arm bearing and produced an outward-acting force. For / its time, that pickup was of an advanced / / design, having the tip . only of a sap / phire stylus fix ed into a small soft iron armature, the latter being pivoted on a SINCE A AND B ARE NOT IN A STR AIGHT LINE . V -shaped spri ng member. A T HIRD FORCE C IS REQUIRED FOR EQUILIBRIUM The needle force was about 30 gms.; a great improvement over the 100 gms. Fig. 1. Dia gram of the forces acting on the then customary. The frequency range, stylus of an offset - mounted phonograph pickup. owing to the small ness of the moving parts, went well above 10,000 cps. From Anyway, for safety sake, this user eased a Hi-F i point of view, the main defect back the adjustment as far as possible, of that pickup was that sapphire did not and if still too strong, sometimes re have the wearing properties then moved the spring altogether. claimed for it, so that "rattle" distortion gradually developed and soon became The Forces Involved serious. Sapphire replacement was un T here may be readers who are not fortunately too speciali zed a job for the clear as to the origin of the inward enthusiast. acting force. In F £g. 1, A is the direc There was also a 'trace of hysteresis tion of the frictional force between the di stortion which seems to be common to record and the stylus. This is along the most moving-iron pickups. (It was not g roove at the point of contact, i.e., tan a moving-coil pickup as some people gential to the record radius just there. think.) In moving-i ron pickups it is es When a pickup with offset head is cor pecially important to keep the armature rectly situated for minimum angular midway between the pole tips. Any lat tracking error, that tangent is approxi eral-acting force tends to displace the mately parallel to the line of the head, al-mature from its central position, and and therefore misses the arm bearing by there is no doubt that the outward bias approximately the same angle that the spring fitted into those pickups was in head is offset. tended by the designer to counter the If the arm bearing is frictionless, it force mentioned. can only pull, and that only in the di It is not known whether the produc rection from the stylus, i.e., in direction tion department kne\;,r what the spring B . Since A and B are not exactly in was for, or how critical its strength was. but in some of the T elefunken Pickups line, there is a tendency for AB to the writer used prior to the war for straighten out, causing the head to move high-quality demonstrations the spring toward the record center unless a third was much too strong. In consequence, outwardly acting balancing for such as upon reaching the eccentric groove at C is provided to ensure equilibrium. the end of the record, the pickup would Normally this third force is provided come out of the groove and skate back automatically by the guiding action' of across the record. Since record surfaces the groove on the stylus. Figul'e 2 shows and sapphire points are vulnerable, this the mechanics involved, and that the condition wa? somewhat less than ideal. point is pushed sideways in the process. This is undesirable. *Voigt Patents, Ltd., Londot., S.E. 26. Apart from springs, the required out- • PAT. PEND . (At present 1\111-. Voigt is in T oronto, On tario.) [C onti'm~ed 01. page 79] 64 AUDIO ENGINEERING • OCTOBER, 1952 See Whllts New ••• Hellr Whllts DiHerent! See Leonard at the AUDIO FAIR A STANDOUT SUCCESS! PREMIER #70 HOTEL NEW YORKER TAPE· SONIC Rms 536·537 A Professional Type Tape Recorder SPECIAL SURPRISES $298.50 net CASE INCLUDED FOR ALL Now Super Horn brings you an entirely new SUPER HORN type baffle that achieves thrillingly accurate reproduction of both high and low frequen· SPEAKER BAFFLE cies. Corner mounting reduces the necessary size of the enclosure, minimizes room reson $80.00 ance~ , and allows walls and floor to act as a horn extension. (15" • • • mahogany) 0 SPECIFICATIONS : Total fold : 180 ; non resonant response down 40 cps (using 12" 15" blonde ••• $85.00 speaker). For 12" speaker ... 15" from corner, 20" along wall, 34" high; for 15" 12" mahogany ••• $75.00 speaker . • . 17" from corner, 21 V2" along wall, 37" high. %" wood throughout, frame 12" blonde ••• $80.00 of solid mahogany, top of mahogany veneer. Altee Lansing Markel 74P Playmaster Duplex Loudspeakers • 12 recordings on one loading . .. 7", 10" , 12" records Model 602A .. . 33-1 / 3, 45, 78 rpms . • Frequency range from 30 to • Automatic shut-off plays 22,000 cycles both sides of record in • Full 2-way system with crossover sequence or one side at 3,000 cycles only . • Sectionalized horn with 2 x 3 • Pfantone "Full Range" aspect ratio pick-up; extremely low dis- . e Power handling capacity: 20 tortion over the entire fre- w. contInuous, 30 w. peak. quency range (40 to 15,000 cps.). e 15" frame; weight, 25 pounds: • Attaches to any amplifier $114.00 ' or radio through A7161 tube preamplifier. Pent ron Reel Extension Kit (X-302) for 10 Yl" NAB reels .... . GE cartridge (golden) 52 ...... The Saturday Review Home Book of Recorded Music ...... MAIL& PHONE ORDERS FIL.LED LANDT ST., NEW YORK 7, N.Y. 25% deposit landt 7-0315 - 9 DEPT. AEIO Balance COD The House Built On Service Send For New 48 Page Hi· Fidelity Catalog AUDIO ENGINEERING • OCTOBER, 1952 63 '" NEW PRODUCTS • Multi-Speed Tape-Transport Mecha q u ency r esponse is within 1 db from 100 nism. Although low in cost, the new Pen to 12,000 c p s. Ma ximu m distortion is 2 tron tape-transport unit is built to a high per cent from 100 to 8000 cps at 5 w a tts. standard of quality and is well suited for installation in custom built home music systems. Push-button control selects either 3 %. or 7'h ins./sec. recording or playback speed. High-speed forw ai'd' a nd ~."...,;;~- \ instrument has a n interna l impedance of ~ approximately 400 ohms. Distortion is less than 1 per cent in the a udio spectrum, rewind. Normally supplied with twin a nd the dial is accu rate within 2 per cent The unit weighs but 10 ounces and m eas track recording head, interchangea bility of its reading. The unit is equipped with ures only 1 % x 213/16 x 1 9/16 ins . RCA of heads permits ready adaptation to a switch which decreases battery dra in Victor Division of Radio Corporation of single-track recording. Mechanical drive when f ull outpu t is not r equired. Housing America , Camd en, N. J. is supplied by four-pole induction motor. is made of splash-proof w e lded a luminum. Bias frequency is 32 kc. Maximum playing time with 7-in. reel is two h ours. Size is • Pin-Point Soldering Iron. Ma ny d elicate • Small Crystal Microphone. Both com 10 '.I, x 9'ri! x 7 in. Supplied with oscillator soldering jobs will be eased by the new pactness and high output are embodied coil. Manufactured by the Pentron Corpo Hexacon Type P-25 miniature sold ering in the new Model 54M3 crystal microphone r ation, 221 E. Cullerton Ave., Chicago, Ill. iron with 'A. -in. r eplaceable tip. Rated at r ecently announced .by The Astatic Cor 25 wat.ts, the iron is designed for con poration, Conn eaut, Ohio. Simple and at- • Plastic Pliers. Engineers and service stant duty on production lines. Ideal for men working with high-voltage circuits will welcome the long-nose p lastic pliers r ecently introduced by General Cement · / use on fine instru ments, small e lectronic Manufactu r ing Company, 919 Taylor Ave., devices, and oth er a pplication s which call Rockford, Ill. Shockproof and sturdily for precision soldering. Available for 110 constructed, the pliers are made of high or 220 volts, either a.c. or d.c. H exacon tractive in styling, the 54M3 measures but impact Bakelite. Now available through Electric Company, 266 W. Cla y Ave., Ro 1 %. in. in dia meter and is only one-half selle Park, N. J. inch d eep. Output is minus 51 db. The leading radio part s distributors. unit is non-directiona l a nd has a response • Applause Meter. T elevision a nd broad range of 30 to 10,000 cps-fiat to 1000 cps; • Precision ReSistors. Accuracy, stability cast stations will welcome availability of gradu a lly rising to 6000 cps. Housing a nd and long life are inherent properties of the portable applause meter r ecently in- handle are combined in a single die-cast the new HycoI' Series E wir.e-wound pr~ frame, with a matching base furnished as cision resistors. Standa rd tolera n ce IS standard equipment. 1 per cent, with tolerances as low as 0.05 per cent available at increased cost. The • Equalizer-Preamplifier. Announced as a companion piece to the new Fisher basic amplifier which was described in these columns last month, the new Model 50-C equalizer-preamp meets the r equirements of discriminatin g a u dio hobbyists for a fiexible audio control unit. Five inputs are troduced by A ir -Tone Sound & Recording units are n on-inductively wound on non Company, 1527 Chestnut St., Philadel hygroscopic ceramic bobbins. Varnish im phia 2, Pa. Consisting of a crystal micro pregnated for moisture protection. HycoI' phone , amplifier, gain control, VU meter, Company, Inc. , 11423 Vanowen St., North a nd power s upply, the e ntire unit is !>Ellf Hollywood, Calif. conta ined. It is a.c. operated. In addItIOn to having many u ses where impartial • Battery-Operated Oscillator. Laboratory judging of contests is r~quired, the me!er precision in the field is afforded by the may be u sed for certam types of nOIse new portable lpw-distortion oscilla tor checks as well. provided with independent level controls, manufactufred by Sou thwestern Indus • Line-Matching Speaker Transformer. as w e ll as two cathode-follower outputs. tria l E lectronics Company, 2831 Post Oak Designe d for use in multiple sound in Sixteen phono-equ a lization combinations. Road, Houston 19, T ex. The Model MB-1 stallations in schools, hospitals, hotels, Loudness control. Self-contain ed power oscillator d erives operating power from a nd other applications where similar re s upply provides d.c. for a ll filaments. AlI self -con tained batteries and covers a fre quirements prevail, the new RCA Ty:pe triode circ uit with tubes shOCk-mounted. quency range of 2 t o 20,000 cps in four M I-12369 transformer affords a WId e The 50-C can be u sed with a ny malte. of decade ranges. Output voltage of 5.5 vol ts range of impedance combin a tions and a basic amplifier. Fisher RadIO CorporatIOn, is delivered to a 2000-ohm load, and the power h andling capaci ty of 8 watts. Fre- 41 E . 47th St., New York City, N. Y. 62 AUDIO ENGINEERING • OCTOBER, 1952 ONLY THE Audio engineers and audio enthusiasts all agree that the INTERMIX 3/522 quality of any sound reproducing system is the sum total of all of its components units. One weak link in the chain dooms HAS THESE ALL the entire system to mediocrity. HIGH FIDELITY In a record reproducing system. the record changer is the FEATURES: first consideration. If high fidelity is to be attained. the record • Intermixes-l 0 and 12 inch Rec changer should be the finest obtainable. ords at All Speeds. • Steady, Constant Speeds - No Rumble or Wow. Consider the COLLARO. The COLLARO Intermix 3/522 • Weighted, Rubber-matted, Rim driven Turntable. was planned for perfection. and was engineered to the most • Four Pole Motor w ith Self-align exacting quality standards. It is truly the high fidelity record ing Oilite Bearings. • No Hum Pickup. changer. and the perfect compl!~ment to any high fidelity • Molded Rubber Drives-No Belts system. to Slip or Replace. See the Collaro at the N. Y. Audio Fair-Room 607 • Stylus Pressure Adiustment Tracks at as little as 3 grams. • Absolutely Jam-proof Opera tion. • Automatic Muting Switch. • Ball-bearing Mounted Turntabl, and Tone Arm • • ' Automatic Shut-off after Last Record. • Tone Arm Clamp for Portable Applications. Base Dimensions: 14 % "x12 %" Depth Below_Base : 2 % " LIST PRICE $65.00 The High fidelity Record Changer for High fidelity Record Reproduction Model 3/521 Fully Automatic Non-Intermix Model L IST PRICE , • • $54.50 R 0 'C K BAR CORPORATION At your Distributor or Write for Details: 211 EAST 37th STREET. NEW YORK 16, N. Y. AUDIO ENGINEERING • OCTOBER, 1952 61 thus leaving hands free for gestures. An modate either two 8-in. speakers or one impressive selection of new cabinetry, in 12-in. speaker. cluding the P ee rage equipment enclosure Permoflux officials have asserted that which nntches in · design the well-known "throughout our demonstrations we will Royale and A ristoc rat speaker cabinets, stress the theme of 'home level' li stening. wi ll fu rther enhance the E lectro-Voice di s By this we mean full-range reproduction play. at a volume level that is comfortable to hear 'Completely assembled hi gh-quality home in the living room. T his is a very important music system which will be marketed at point to the great majority of hi-fi li steners prices that complete with conventional and we feel that it deserves a great deal of radio-phonographs will be shown by The stress." (We do , too . See "Observations on Sound Workshop, a new company recently demonstration technique," page 84. ED.) formed by E lec tronic WOI'kshop Sales The Gately D evelopment LaboratOl'ies Corp., New York, and G & H Wood Prod will present for the first time publicly its ucts Co., Brooklyn. A lthough various line of corner speaker enclosures known as models of the Sound W ol'kshop line may The Superhorn. Available for 12- and IS-in. HIGH FREQUENCY REPRODUCERS bear li ttle resemblance externally, inter- MODELS 4408, 4409-600 CYCLE TWEETER , Respon se 600·15,000 cps . Ideal for 2 or 3· way systems as Tweeter or mid.ronge speaker where low crossove r frequencies are desired . EXCLUSIVE "reciprocating flares" de sign results in wide angle distributi on. Use with am· plifiers up to 40 watts. MODEL 4407 - COAXIA L SPEAKER ADAPTER. Convert s con ventional 12" cone speaker into a wide-range coaxial reproducer in 0 few minutes. Installation is extremely si mp le and results i n a dual speaker system at relati ve ly low cost. Model 4407 in cludes Model 4401 Tweeter. M------MODEL 4401 - 2000 CYCLE TWEETER, respon se 2000·15,000 cps. Effi cie nt and nally there are several co mmon denom economical for extending the inators. A ll , fo r example, wi ll contain an of any good 8-15" cone amplifier with at least ten watts rated out sp~aker to 15 , 000 cps. EXCLUSIVE "reciprocating put, a three-speed W ebcor record changet·, flares" design assures wide a GE dual-stylus magnetic cartridge, an angle dispersion. Use in 2 or 3.way systems where crossover FM-AM tuner, and a Jensen high-quality in th e 2000·5000 cps rang e speake!". is desirable. f or amplifiers up to 25 watts, woofers 6·160hms. In merchandising the Sound Workshop direct-radiator speakers, these enclosures . ------line, emphasis will be placed on the suit are characteri zed by hi gh acoustic damping, 4402 - WIDE ANGLE ability of the val'ious units for "Aunt DUAL TWEETER. The high efficiency, and exceedingly smooth re most ve rs atil e repro· Minnie," a mythical character who sprang sponse. In demonstrating the Superhorn du cer ever ovailable. from the brain of Richard K. Snively, every effort is going to be made to dupli Use of TWO i ndepend· e nt drivers pe rm it series prominent advertising executive, in a note cate a typical home installation. or parallel co nn ection to £'s LETTER S column several months Stromberg-Carlson, participating in its for matching 4·16 ohm speakers. ago. Throughout the SW di splay at the For amplifie rs to 50 watts. Can first Audio Fair, will feature an animated be conne cted for medium or wide Fair will be "MI NNEHIFI" signs. showing of the new "Custom 400" lin e of angle distribution. For 2 or 3·way system s. Response 2000 · 15,000,...! The P ermoflu x exhibit will be highly music-reproducing equipment. Due largely animated, including a binaural demonstra to the publi shed comments of noted musi CROSSOVER NETWORKS tion as well as introductory showing of a cians, Leopold Stokowski in particular, the number of new P ermo flu x speaker enclo Stromberg exhibit is certain to stimulate ~1~~~ILN{,4~ETWgREK~~EnN;l sures. Among the latter is the new Model deep interest from lovers of fin e music. fective and economical unit CH-1 6M corner baffle which will accom- David Bogen Company, Inc., along with preventing frequencies below a new FM-AM tuner and a new line of 2000 cycles -from entering the Tweeter circuit. Protects the Tweeter and reduces overlap in the crossover range. Includes built·in volume control. ~------~ MODELS 4410, 4420-L/ C CROSSOVER NETWORKS. Segregates highs to the Tweeter and lows to the woofer. Reduces overlap response in Tweeter and woofer. Model 4410 for --""~~'" 600 cycle reproducers, e~-i ~.~_:~ .. ".. r, 4420 for 2000 cyc l e tweeters . Con be used ~ ~ toge th er a s a network for 3·way systems. Vol. ;..:_ ~'~ ~ I) - - <) ~ ume controls includeg, r ~- . -" ;:::A ------.. ~ ~ Write for literature describing _ [ . '8",12", and 15" extended range, 'toaxiol ond woofer type cone speaker$, " Address Desk A·IO. high-quali ty amplifier s, wi ll introduce a de luxe intercom system designed especially for use in homes. Known as the H ome Com LO~NC muno-Phone, the system contains many 80 SO . KENSICO AVE .• WHITE PLAtNS. N. Y. [Continued on page 86 ] 60 AUDIO ENGINEERING • OCTOBER, 1952 HEADQUARTERS FOR NEW IDEAS FM, Records, Tape Looking for used improperly, or in an application for ways to mount speakers. Ideas? Why every· ideas in FM tuners, or equipment used in which it is not intended. As a matter of issue of HIGH-FIDELITY is filled with them! conjunction with records and tape? Or fact, we have had a great number of letters ideas for installing and using them? from readers who found that the Tested 'I1t1!1 You are particularly in All over the Country, amateur enthusi- in-the-Home Reports cleared up essential vited t.O visit us at the :New York Audio asts and professional designers are working points about equipment which were not Fair, Hotel New Yorker, October 29 to out new and constantly improved hi-fi covered in manufacturers' instructions or November 1. The FAS-2 audio system, to installations. They range from simple, func- literature. be described in HIGH-FIDELITY for No tional designs to those of strikingly decora- , Hi vember, will be on demonstration in Rooms U,14 Lij tive appearance. Some introduce new types _ mill...... _ There is a great deal of en- 552 and 553. If you want to hear some of of equipment; others represent unusual, gineering data available on the subject of your own records on the FAS-2, bring special-purpose arrangements. They are re- acoustics, but very little of it can be applied them in. We'll be glad to play them for ported in elaborately illustrated articles in to the practical problems of home installa you. That is the best way to compare re HIGH-FIDELITY Magazine, described in the tions. A notable e)Cception is the series of production from the FAS-2 with your own "Noted with Interest" columns, and dis- ·articles on speaker systems and room acous system. Our editorial staff, now including cussed in the "Re ------Charle. Fowler, Editor HIGH-FIDeliTY Magazine 1310 Publishing House, Great Barrington, Mass. Please enter my subscription to HIGH-FIDELITY for which I enclose: o $5.00 for 1 year (6 issues) SAVE $1.00 o $10.00 for 3 years (18 issues) SAVE $8.00 Hiflk;1ideliflj (Single-copy price $1.00) MILTON B. SLEEPER, Publtsher Nome...... Address ...... "THE MAGAZINE FOR AUDIOPHILES" Foreign postage: Add $1.00 per year. AUD.IO ENGINEERING • OCTO,BER, 1952 59 AUDIO engineering society Fourth Annual Convention Preview of the Program 1952Audio Fair ITH THE INCREASE in the length of the AES Convention from three days ' to four, more time is available for the ORE MANUFACTURERS of audio equipment will introduce Wpresentation of technical papers-the principal function more new products at the 1952 Audio Fair than have ever of the annual meeting. As heretofore, papers have been grouped Mbefore been shown in a single public di splay. to facilitate attendance by those who have interests primarily Beginning October 29 and continuing through November 1 in centered in a specific branch of the audio field. Sessions over the the famous Hotel New Yorker, the Fair will serve as the demon four days have been arranged to cover recording, new develop stration stage fOI' li terally hundreds of amplifiers, speakers, tun ments, components, intermodulation distortion, speech input sys ers, recorders, and other audio devices which are but one step tems, design data, and home music systems. Because of the gen from the designing table, and which may not appear in dealers' eral public interest in the latter subj ect, this sesson is scheduled showrooms for months to come. As in previous years, admission for Saturday morning, since many of those who would find some is free to all persons with an interest in audio. thing of value in these papers might not be free to attend during Typical of equipment which will be shown at the Fair, although the week-day sessions. not yet available commercially are two unique recorders which According to F. Sumner Hall, Society vice-president and will be featu red in the exhibit of Harvey Radio Company, major chairman of the Convention Papers Committee, the program is New York jobber. One, the Cub Corder (see Cover), is a bat complete, and consists of the following papers: tery-operated tape recorder which affords complete operating mobility to the user. The other, known as the Minifon, is a Ger man-manufactured miniature wire recorder. Small enough to fit into an average overcoat pocket, the Minifon also is battery op erated, Considering its small size and its operating character istics-two-ancl-one-half hours of recording on a single spool, and WEDNESDAY, October 29 25 hours from one set of bat teries-this tiny unit brings 10 : 00 a.m. Annual Business Meeting of the Society. into reality an instrument (This meeting is open only to members.) which can be regarded only in the light of fantasy until it 10 :30 a.m. Technical Session is seen. Altec Lansing has selected RECORDING the Fair as the firs t major BINAURAL DISC RECORDING, Emory Cook, Cool~ Laborat01'ies public showing in the East of METHODS OF MEASURING SURFACE INDUCTION OF MAGNETIC its new Type 601A and 602A TAPE, J. D. Bick, RCA Victor Division speakers, also the new Type A NEW PROFESSIONAL MAGNETIC RECORDING TAPE Edward 606 corner cabinet. Remark Schmidt, Reeves S oundcraft Corporation. ' able performance of these units makes them a matter 2 :00 p.m ...... Technical Session of newsworthy interest to en gineers and hobbyists ali ke. NEW DEVELOPMENTS The 601A and 602A repre CONSTANT-CURRENT OPERATION OF POW ER AMPLIFIERS Howard sent distinct improvement T . Sterling, Waveforms, Inc. ' over the famous Altec Lans A NEW POCKET WIRE RECORDER, Oliver Read, Radio & Tele ing 604B, which has been a vision News staple in the audio field for MUSICAL T HERAPY, R. L. Cardinell, NIagnetic Progra·ms, Inc. a number of years. SOME CONSIDERATIONS REGARDING . VOLUME PRODUCTION OF Electro-Voice is another ELECTRONIC MUSICAL I NSTRUMENTS, George H. Hadden, prominent manufacturer to Minshall-Estey Organ, Inc. schedule showing of an im- GUNSHOT REINFORCERS ,AND SYNTHESIZERS, J. L. Hathaway and pro v e d speaker R. E. Lafferty, National B1'oadcast'ing Company. this one, for public ad d r es s use, is known as the Com- , pound Diffraction Proj ector System. Unique and exclu sive, the CDPS of fers increase of ar THURSDAY, October 30 ticulation index for speech reproduction 10:00 a.m...... , Technical Session and two-and-one· half octaves in COMPONENTS creased range for THE DEPOSITED CARBON RESISTOR, Llewellyn Bates Keim, Aud·io m u sic. E lectro C onsnitant Voice also will in ELECTROLYTIC CAPACITORS-WHY AND WHEN, Mark VanBus troduce a new p.a. kirk, P. R. Mallory & C0111pa,ny, Inc. microphone known CHOICE OF TUBES FOR AUDIO CIRCUITS, W. R. Ayres, RCA as the Lavalier. As V icto1' Division its name implies, REVIEW OF NEW PRINTED CIRCUIT DEVELOPMENT AND AUDIo the Lavalier is a FREQUEN CY ApPLICATIONS, Arthur W. Kelly, J r., Photocirwits small unit which C o1'poration. can be suspended [ Continued on page 82] necklace - fashion, i 58 AUDIO ENGINEERING • OCTOBER, 1952 You are Invited to Attend the Fourth Annual AUDIO FAIR Sponsored by the , AUDIO engineering society in conjunction with its Annual Meet.ing and Convention TODAY and AUDIO TOMORROW of utmo'st interest and importance to government and military agencies. Broadcast Engineers, Recordists, Sound-on-Film Men, Publ ic Address Operators, Audio Hobbyists, Dealers and Di stributors, and lovers of H IGH QUALITY and HIGH FI DELITY music reproduction. YOU WILL SEE and HEAR industry-wide displays and demonstrations of the latest and BEST AUDIO and HIGH FI DELITY equipment, com ponents, and accessories. AGAIN UNDER ONE ROOF Hotel New Yorker, New York C,ity, Oct. 29, 30, 31, Nov. 1, 1952 Filth and Sixth Floors ADM ISSI'ON FREE to all Exhibits Registration at 5th and 6th 1I00r booths EXHIBIT HOURS Wed.-October 29 ...... 11 :00 A.M. to 9 :00 P.M . Thurs. October 30 ...... 10:00 A.M. to 6 :00 P.M. (AES Banquet at 7:30 P.M.) Fri ., October 31 ...... 10 :00A.M. to 10:00 P.M. Sat., November 1 ...... -: . . . . 10 :00A.M. to 5:00 P.M . For further information and banquet reservations, write Harry N. Reizes, Fair Manager, Room 510, 67 W. 44th St., New York 36, N. Y. MUrray Hill 7-2080 AUDIO ENGINEERING • OCTOBER, 1952 57 Again this should sound "clean" 011 your We want to 'find out how much inter monitor and be a smooth sine wave 011 modulation distortion is appearing near INTERMODULA TlON your 'scope. the 5,000-cps note due to the lOa-cps Now for the distortion measurements: tone. Set voltmeter at HI, and read it Gradually increase the lOa-cps tone, un (starting with high range, 10 v, xl). DISTORTION til the voltmeter (IN) reads 8 volts, S uppose it shows 1.1 volts. Now switch which previously produced clean output. to LO, and reac!. Let's say it is 0.05 volts. W e now have an amplifier playing a The intermodulation distortion for this double tone--8 volts at 100 cps, and 2 case is 0.05/ 1.1 = 0.055 or 5.5%. "clean" at 100 cps. Now turn down the volts at 5,000 cps at the same time.'" It is a good idea to make tests at dif volume of the lOa-cps note to zero; and ferent outputs; the distortion will be less turn up the . 5,000-cps note to an output 11 (This is not absolutely exact ~v hen m easwred in this manne?', since the pl'esence for lower output powers. You may be one quarter that of the lOa-cps note s urpri s~d to find out how few watts your 10 of the · SOOO-cps tone will ??lal~e a slight "clean", in this case 8/ 4 = 2 volts . increase ave?' the voltt?/1.e of the lOO-cps ton.e when the two m'e combined. I-J owever, 10 With 8 volts at 100 cps and 2 volts at p?'ovided this sa?-ne method is ttsed consist 5000 cps, the high frequency is 12 db down 2 ently, ?'esnlts may be co·mpared with rebi z in volume from the low frequency. o 1 abil-ity. ED.) ;:: / / ,,1/ 0:1 5 ' I ~ I / I , i5 ~~ I z 10 o ~ ~ , " "./ //, -' " / I :::> 5 g 3 ,. ". 0: " 11 I ...OJ / / ;, 2 7 I ...z OJ r7f 17 u 1 ffi - /.V / "- ~~ P %.5 2 5 10 20 WATTS OUTPUT Note chonoe of scole, 3% to 5t:, Inter mod. Distortion. A.)6V6sln9Ie pentode , no feedback , output trans." i B.)6V6 M II ,tOdbfeedboCk. .. M C. )6L6G push · pull pentodes, no feedback, trans.1t2 D.) 6L6G " ",14db feedback, " II E.) 807 trlodes -Wllliomson,-trons.13 ·F.) KT-66 " II IransAt4 Fig. 8. Typical I M distortion curves taken with various types of amplifiers. " 10 watt" amplifier will do with low dis tortion. General Comments and Conclusions The whole problem of intermodulation di stortion is relatively new- you can use frequencies and ratios to suit your self. There is no accepted value of allow able di stortion. There a re even no gen erally r ecognized standards for the high or low frequency or fo r their l-elative ratios. As indicated before, a 4: 1 volt the professional's tape ratio ( 12 db) of low to high tone is used by several, and' a generator pro recorder for your home viding 100- and s,OOO-cps tones can be Here is a precision-built tape recorder, a useful additional piece of equipment fo r amplifier testing. A high-sensitivity modified for use and enjoyment in your tube voltmetel-, w ith low ranges, is al home or office. Handsome in its blond or rich ways a handy piece of equipment. It will dark mahogany €abinet, MagneCordette's 111 ~as ure pickUp output voltages, for ex crystal clear sound reproduction is amazing. ample. MagneCordette catches every sound Perhaps after measuring some of your exactly as originally produced. Record pet amplifiers, you w ill decide to take some drastic steps to reduce di stortion, your favorite AM or FM radio program, such as increased feedback, or some the voices of your family and friends. Start other such device. You will probably your family music library now, for find, with the tests outlined, that ~ sin enjoyment in the years to come. gle pentode at full I-a ted output WIthout feedback will show over 20 pel- cent Here is professional tone brilliance at a price you can distortion and as low as 4 per cent with afford to pay. MagneCordette is priced at only $385. For proper feedback. S ingle output triolles descriptive literature and a demonstration, see your local may have 10 per cent distortion with distributor, listed in your Classified Telephone out feedback, ancl below a ,s per cent Directory under "Recorders". with suitable feedback. Push-pull ampli fiers will have (maybe) one-fifth the distortion of single-ended ones. Good magnecord, inc. Depl. AE 10 output transfonl1ers show up best,. as 225 West Ohio Street, Chicogo 10, Illinois is already well known. A few tYPIC".! measurements are plotted in Fig, ~. 56 AUDIO ENGINEERING • OCTOBER, 1952 CREDIT TITLES IMPORTANT TO YOU? ,I Is your Qudio system ooing justice to your experience? Maybe .~" i the Boss can't see buying a compl'etely new system ... Why not I bring your system up to par with the kind of audio that sells the program and the sponsors' products? " Transmitting intelligible sound is an admirable accomplishment .. .. sound that entertains, emphasizes, and sells ... is easily within your reach - YOUR THE CINEMA 4031-B THE CINEMA 651 7-D PROGRAM EQUALIZER AUDIO VARIABLE LOW AND HIGH FREQUENCY FILTER IS ENTITLED Used in all types of sp4ilech ir1put equip TOTHE Cut off characteristics ideal for shorten ment. The 4031-B corrective equa'lization ing frequency range; providing sound saves on recording retakes; improves BEST effects, such as telephone, whispering, tonal quality; provides emphasis when spooks, etc. C1ickless control allows in needed during the program. Widely used sertion upon cue. Used in Motion Pictures, in Motion Pictures, T-V, Recording and T- V, and Scientific laboratories. Miltary Communications. Write for descriptive literature. N. Y. Stock-Audio 8. Video Products Corp. '. 730 Fifth Ave. • PLaza 7,3091 CINEMA ENGINEERING COMPANY 1510 WEST VERDUGO AVENUE, BURBANK, CALIFORNIA Export Agents: Frazar & Hansen, lId, • 301 Clay Street· San Francisco, Calif., U. S, A. AUDIO ENGINEERING • OCTOBER, 1952 55 there was no difficulty with this prob lem. But when the gain approached unity, even though there was some de 1tellJ-1t~ , , , lay involved which should prevent feed back, residual noise on the tape often products of the built up to feedback proportions, and 'Itt would occasionally simulate a tone. The frequency encountered in this case was CINEMA ENGINEERING COMPANY around 12,000 cps. A lO-kc low-pass filter cured the situation almost entirely. are distributed by The gain could then be greater than unity. for short periods, until it over loaded the amplifiers. At the slower speed, it was not necessary to add a I) ~~!~~~ c~.~!~~o separate filter to reduce the high-fre 730 Fifth Avenue, New York 19, N. Y. • PLaza 7-3091 quency response-the recording equal izer was simply switched to the 15-111,/ Exhibiting at the Audio fair - Rooms 6 J4 & 6 J 5 sec. position, The lack of high-frequency response at the slow speed provided all the filtering necessary. As will be noted in listening, there is some frequency distortion when allowing more than about three repeats, The lows are slowly lost, and the effect becomes almost Pt,,P~l'al/e/eti "tinny" if allowed to continue. This may or may not be desirable, depending on the effect to be created. In controlling the level of the play back, it was noted that when operating near the point of unity gain, the usual graduation of 2 or 20 db per step was PRES E" too much, and would throw the system into feedback. It was found that 0 db-pel--step faders would give' the de- , sired gradation. This would make it seem stepless to the ear, and would permit working much closer to the point of unity gain without incurring the dan ger of so-called feedback or of spilling over into positive gain in the loop. Any change of level should be made slowly if there is a signal in the system. If a change of more than 2 db was made during the transit time of a given point on the tape, this change will be repeated for as many ti mes as the sound takes to decay. This gives rise to thumping at the slow speed or flutter at the fast speed. By using a "filter mike," additional and almost amazing effects can be cre ated. Many ethereal effects are possible, and they can add charm, humor, rever ence or macabre, depending on the type DUAL CONCENTRIC of show involved, For instance, if a set of chimes- or a vibraharp with the LOUDSPEAKER SYSTEMS dampers off-is played with a soft mal let and the sound run through the echo Now experience the amazing LF components avoiding inter· system, the effect is "heavenly." An lis tenability of wide range ference at crossover. HF hom additional feature of this system is that response in perfect balance. Hear formed by machined center pole the recorder is still being used to record the world famous Tannoy Dual and LF diaphragm, these com· the program in its entirety, As long as Concentric Loudspeaker System, bined with a special throat insure providing optimum fidelity at an y the playback fader is kept closed, the correct HF match.lnt ~ rm odulation recorder functions normally and cap level from the audibility thresh· . product less than two percent. old up to full room volume. tures the main prpgram. \i\Then the echo Features of the Tannoy System Hear It to appreciate it! Write effect is needed, merely open the fader include: for free brochure and name of to the predetermined position, and there Substantially flat response from neares t distributor today. 12" is the echo, This too, becomes a part of 40·20,000 cycles per second. Can· and 15" types, handling 15, the program material. When the echo is centric sources for bOlh HF and 25 watts. no longer needed, the fader is closed, and the recorder is left runll ing to cap SOME DISTRIBUTORSHIPS STILL AVAILABLE ture the rest of the program, Hear Tannoy at the With a little practice, any operator AUDIO FAIR ' BEAM INSTRUMENTS Rm. 603 should be able to familial-ize himself TAMMOY Hotel New Yorker with the techniques involved for the various effects, and indeed, to create BEAM INSTRUMENTS CORPORATION new situations to suit his own require NEW YORK 1 NEW YORK . 350 FIF'TH AVENUE .ments. 54 .. AUDIO ENGINEERING • OCTOBER, 1952 speed of the wire. This is obviously a rather cumbersome method and does not You can't buy better performance provide the degree of fl exibility some times needed. In the syst,em outlined at any' price! here, the reverberation time may be ~ changed at will with one control ; in the old system, it might require up to ten adj ustments. The amount of attenu ation necessary can be determined quickly by experiment. In the fi rst setup of such a system for a dramatic pro gram, it is desirable to experiment with the amount of attenuation, and when the desired effect is obtained, simply log the setting fo r use in that particular show. In trying to duplicate certain locations known to listeners, it might be helpful to remember which function duplicates which feature of the reverberation. The size is most generally indicated by the time delay, whereas the characteristics of the refl ecting surface will determine the rate of decay. A lso, the tonal quality of the refl ected sound may be altered by the nature of the material. A soft sub tance will generally absorb the high h eq uencies and cause the sound to be "muddy" or lacking in brill iance. A tone control may be helpful in further enhancing the effect of reality. It is astounding how an otherwise good pro duction can be ruined by poor acoustical effects, such as, in a live studio, the echo of walking feet when the scene is supposed to be outside. Two-Machine' Set-up No mention has been made so far about the use of two machines as shown First wide range diamond-and-sapphire combination in the diagram. One machine, running delivers frequency response from 30 to 15,0.00 cycles. at 15 in./ sec" is capable of many real Tracks all 3 speeds at 6 to 8 grams istic effects. By proper manipulation of the fader, almost any desired acoustical effect can be approx imated, ranging H IS new I-mil diamond wear out. Remember-when from large caverns to very small hall T and 3-mil sapphire* stylus you replace a stylus assembly ways. But at times a lack of fullness that assembly lengthens the life of in a General Electric cartridge, defi es realism will be noted. Better re sults can be obtained if a second ma your records and delivers tone you replace every component chine, running at 70 in./ sec., is used. reproduction unsurpassed by that is affected by age or wear. The two machines together- if properly any make on the market. A new stylus assembly means, mixed- make the effect come alive. In this event, the sound is fed back at two The replaceable stylus is of in effect, a new pickup. different delays, with both machines re the famous G-E "Baton" de Ask your G-E dealer about cording the original sowld as well as sign. Multiple damping blocks the Golde n Trea sure ca r · both playback outputs. With both of them delaying all the sound, the effect filter out harmonic distortion, tridge, or write us for the near becomes almost overwhelming. The needle talk and needle scratch. est sour ce of supply. General 70 -in./ sec. machine cannot be used to There are no moving parts in E lectric Company, Electr01zics the fullest extent unless it is used alone, or the result will be an uni ntell i this cartridge - no,thing to Park, Syracuse, New York. gible mass of sound, completely masking · SYlllbelic the original. If used alone, however, it is effective if the illusion of vastness is Send for these new cata logs . .. needed. W hen used in combination, the III 1mIs::i ~ two machines have been used to simulate Mammoth Cave, or, ' :with moderation, G eneral Electric Company, Section 5492-15 t'A e sewers of P aris. In this case, the Electronics Park, Syracuse, New York water provided the proper effect neces Please send me the items ch ecked: sary for realism, and listeners inquired o Pho no Accessory Catalog 0 Wide R ange StylUS Folder as to whe]'e "]'ecordings" of this effect I were obtained. NAME ______ADDRESS ______Notes on the Use of the System I CITY------______S TATE ______A few of the difficulties which can be o I encountered may be of interest. T he big gest trouble was that of actual, or ap ~ parent, feedback. At high levels of GE NERAL _ ELECTRIC attenuation around the ]'ecording loop,. AUDIO ENGINEERING • OCTOBER, 1?52 53 • Echo Effects with a Tape Recorder R. S. HOUSTON':' Applying the principles of a reverberation generator to conventional tape machines to provide - in a limited fashion - a variety of effects not usually available. I NCE THE ADVE NT of tape recorders sound, although generall y of lesser in in producing artificial reverberation. with a separate playback amplifier tensity than the original and changed First, that of providing a suitable delay, to permit monitoring of the tape S sli ghtly in quality and timbre, can be for the sound originally emitted before while recording, enterprising engineers louder than the orig inal if the source have seized upon the delay introduced it is heard again; and second, providing is la rge in relation to the listener and if a suitable decay period before it wi ll by the playback as an effective means of ·the configuration of the reflecting SUl·- producing, a rtificially, the effect of some fade into inaudibility. The first is pro sort of reverberation chamber. The use face is such as to foc us the sound back vided by the variable speed at which fulness of this effect in dramatic work to the li stener. This effect is familiar the recording is run. On the 70 in.jsec. or even on some types of spot annouce to anyone who bas heard his voice re speed on the machine used, the delay ments is, of course, obvious to those flected off a cliff, or even from a nearby from the recording head to the pl ayback fo rest .. who have worked with such effects to head is approximately 0.75 sec., while at any extent. While the principles outlined Reverberation is simila r to echo, ex cept that it is the 11'Iuttiple return. of 15 in ./ sec. it is just one half as long. here are not intended to be taken as According to Tall,! the ear, or the. br~in original, there are some concepts which sound from many points of reflectIOn, all at different distances, so that the center associated with the ear, IS 111- the author thought might be of more sounds return at different times. This capable of di stinguishing between two than academic interest to the eng ineer effect is produced also by the same sounds that occur closer than about 0.14 who has been called upon to provide thi s sec. apart. T herefore, the 0.375-sec. facility. The recorders used in the origi sound being bounced ba9k and forth between nearly parallel surfaces, If some delay provided on the faster speed see.ms nal experiments were two Presto PT- of each refl ection is returned to the 900 machines. They were rack mounted to be about optimum. The decay pen od li stener. T hi s is often noted in hallways, is provided by the fader on the console. in the control 1'00:11, immediately behind indoor swimming pools, and-as the the control console, for easy access by Consulting the diagram, it is seen that ultimate-in water-filled caves, espe- the operator. One machine was set to the circuit for anyone machine is a ciall y large ones. . run at 70 in./sec., and the second ma feedback loop. Shch would be the case, A n additional effect noted 111 rever were it not fOl- the delay occasioned by chine was set at 15 in.jsec. Their re- ' beration is the constant attenuation of spective inputs were bridged across the the tape in running between the record each successive wave of sound that is head and the playback head. All sounds output of the console, so they recorded returned to the source. A lthough theo that leave the console are impressed on everything that came from the console. retically the sound will bounce around The two outputs were connected. to in a closed area forever, it is eventually the recorder, so when the original sound separate faders in order that they might absorbed and lost as heat, in actuality. is played back, it becomes part ~f the be individually cgntrolled as to volume. output of the console again, and IS re Long before this occurs, how~ver , it has The fadel·s then actually control the become inaudible. It is the period of time impressed on the recorder. ThiS process decay period, as will be expl ained later. from the incidence of the sound to the repeats continuously until the sound h ~ s The diagram, Fig. 1, illustrates the completely died out.. If ~h~ total gam point of inaudibility th.at ~ilI c.oncern set-up used. us her e: The reverberatIOn time IS gov and loss around the CIrCUIt IS Ul11ty, the sound will be reimpressed on the tape Theory of Operation erned by two main factors-the absorb tion coefficient of the reflecting surfaces, with the same volume as the original, A short review of the principles of and the di stance between them. Other and it will never die out. Suppose, for reverberation and echo, wi ll clarify the factors which enter in a smaller degree example 3 db of net loss is inserted by problems involved and p e rn~i t better are the original intensity of the so,!nd m ean s~f the fader. This will put the understanding of the use of tillS system. and the dispersion of the sound; I.e., second impression of the sound at a l ev~ l Echo is a single return of a sound to how much of the sound striking the re 3 db lower than the original. When It its source, generally by being reflected flectinCT surface is not absorbed, but sent aCTa in comes 'around, it will have lost 6 from one or more surfaces so spaced . in the" direction of another reflecting db, and so on. Since . for broadcast and angled as to direct th ~ so ~nd back surface or back to the point of origin. use, the minimum ehectlve usable level in the direction from whi ch It came, Assuming a 'fi xed decay time, it will is about 30 db below 100 per cent modu much as a mirror does with li ght. This naturall y take a loud sound longer to lation the sound will make ten reverber become inaudible than a soft one. ation; before being lost. At 15 in./sec. * 2921 N . W oodstoell , Philadelphia 32, which would mean a delay time of 0.375 Pa. . (formerly Chief Engi1leer. KBNZ, La With these facts in mind, it is easy to see the two main problems that arise sec.-it would take the sound 3.75 sec. J1t1~ ta, Colo.) to reach 30 db attenuation. This is a very long decay ti~e and s houl ~ be long enough to accomplish any deSIred pur pose . 15 in/sec • Putting Theory to Work Fig. 1. Block diagram In some of the original magnetic-tape TAPE TAPE of method of con MACHIN E MACHINE reverberation "chambers," a wi r ~ re necting two tape re corder was used with some ·ten pickup corders in a control coils spaced at intervals along the ~i r e. PROGR AM 8US room to provide re OF verberation effects. Each of these went through a van~b l e TRAN S MITTER attenuator so as to val-Y the decay time. 1 The delay was varied by changing the BRIDGING • MIKE '--__--' OUTPUT 1 J oel Tall, "Tape editing." AUDIO ENGI-i NEERING, May, 1952. 52 AUDIO ENGINEERING • OCTOBER , 1952 ', I with the New CUB CORDER Portable Tape Recorder ------~ You will See it for the First Time at the AUDIO FAIR, Hotel New Yorker, HARVEY EXHIBIT - ROOM 631 Here is another 'new' in the annals of eliminating a time-consuming operation. Harvey's wide,awake policy to be on the Frequency response is from 200 to 6000 constant lookout for new developments, cycles/sec. at 7Yz" /sec. A sensitive dynamic new ideas, and the finest of new products. microphone is furnished wHich 'doubles' as This time it is a battery-operated, light an efficient earphone for playback. An out weight recorder. More compact than a port put is provided for playback through an ex able typewriter, yet with storage space for ternal amplifier with high impedance input. three full 5" reels of tape, an empty take-up The Cub Corder has made tape recording reel. and a microphone. possible in fields which have thus far been A rechargeable, non-spill wet cell and a denied its advantages. Weighing only 12 Ibs. 67Yz volt B battery furnish power for the 14 ozs. in its handsome luggage-tan leather motor, erase oscillator, and amplifier. The grained case, and measuring only 5% x 13%. Cub Corder may be used continuously for x 12 %. inches, it finds ideal applications in 2 hours before it becomes necessary to re broadcasting and TV, industry, profession!;;, charge the wet cell. Two models are avail schools, government agencies, research or able: for 3 % and 7 Yz" / sec. or for 1 % and ganizations, news syndicates, and many other 3%" /sec. Either may be obtained for single fields as an indispensable time and money saving tool. or dual track recording. At 1%" /sec., the , Cub Corder provides one hour of uninter The Cub Corder may be used anywhere, and rupted recording on a 5" reel. under any circumstances. Interviews may be All operations and controls have been sim recorded, notes taken, reports and corre plified. Provided with fast forward and spondence dictated, news events covered ... normal speed, specific recorded material in the air, on the ground, or at sea ... aboard can be quickly located. Recording operation ship, in a car, a train ... anywhere. The is remotely controlled by a push-button scope is practically unlimited. conveniently located on the microphone. You press to record, and when the button Complete with microphone / ear phone, 5" reel of tape, empty is released, the recorder stops. Professional take-up reel, batteries, tubes, and type erase is automatic when recording, instructions. NOTE: I n view of the rapidly changing market conditions, all prices shown are subiect to change withcut notice and ore Net, F.O.B., New York City. AUDIO ENGINEERING • OCTOBER, 1952 51 I with the New MINIFON Miniature Portable Wire Recorder ~------~- You will See it for the First Time at the AUDIO FAIR, Hotel New Yorker, HARVEY EXHIBIT - ROOM 631 No bigger than an, ordinary camera, the weighing only 2 Ibs. 7 ozs., it may be con· Minifon . is just about the world's smallest veniently carried about for use anywhere, sound recording instrument. Everything is and under all conditions. The Minifon will self· contained. Powered by a standard 1 Y2 record the merest whisper, and play it back volt A battery, a standard 30 volt B battery, with amazing intelligibility and distinctness. and seven Mallory RM-4Z Mercury batter· A simple volume control adjusts both the ies, this midget device records, rewinds, recording and playback levels. erases, and plays back through either an external amplifier* or a pair of stethescope The Minifon is a valuable tool. Doctors, type earphones. lawyers, engineers, business e~ecutives, salesmen, teachers, ,scientists, reporters, se· The Minifon is capable of 2Y2 hours of curity agencies and a host of others will uninterrupted recordings on a single reel of find this instrument an indispensable aid in wire. Once recorded, the wire may be reo their work, to be used in offices, in cars, wound and played back instantly, or it may in airplanes, in trains, on board ship, or be stored or mailed for playback at some even In subways ... anywhere ... wherever other place or at another time, and as often and whenever interviews are to be held, as may be required. When the recording is notes are to be taken, or records are to be no longer desired, the wire may be erased made. There is hardly a job which wouldn't for another recording. In this way the wire benefit from ' or which wouldn't be easier may be used over and over again. with a Minifon. The useful applications of the Minifon are practically unlimited. Measuring only 1 % x 4% x 6% inches. and . Complete with microphone,stethe. scope type earphones, 1 hour spool RECORDING WIRE of wire, tubes, batteries and instructions. On spools, in dust· % hour ...... $ 7.00 proof plastic con· 1 hour...... 9.00 tainers suitable for 2hour ...... 17.90 mailing. 2% hour ...... 21.50 '::'Output for external amplifier is transformer coupled for 500 ohm input. VISIT THE AUDIO· TORIUM. Come in and visit our new sound department ••• all thes'e items and many more on work· ing display at all times. 50 AUDIO' ENGINEERING • OCTOBER, 1952 / ? • ~ ? • . , How often have you wondered w.hether the needle in your pickup, the stylus in your cartridge, has not already outlived ,its usefulness; whether ? • your costly records were not being srowly, silently, but surely worn down and abraded. Nothing is permanent ... not even a diamond, HOW LONG? and when ~ stylus is worn, it will take no time at HOW LONG? all for a recora to be ruined. Y~u ~ay have tried squinting at a ,stylu.s tip HOW LONG DOES A through a magnifier or a microscope, b~t it takes a boatload of expe,rts to figu~e out when it's STYLUS LAST .' •• 'gone'. before it begins to There is a new, easy, and foolproof way. You can't miss. You can discover a wearing stylus before it contribute to distortion, begins the damage. And it will save you loads of and to take its toll of dollars in favorite records. valuable records, in See It for the FIRST TIME at the HARVff Exhibit irreparably dam,aged grooves. Find the answer to this perplexing problem at the ,, ,/ / / I There'll be more I Surprises in store J \ at the \ Harvey Exhibit \ \ , Don', Miss It! "- , ...... -----,.,.,. HARVEY's new HIGH FIDELITY AUDIO CATALOG . will be distributed FREE in Room 631 AUDIO ENGINEERING • OCTOBER, 1952 49 ARROW'S fabulous, n~~ o . e II I was designed for Y.9I1.- Yes, Arrow's new Audio Center was created with YOU in -mind. Whether you are a dyed-in-the wool High Fidelity Fan or jus ~ a neophyte" an Audio 'Engineer with design and development problems, or a JENSEN ,,~, Professional or Industrial Sound User-you' ll find exactly what LEAK you're looking for at Arrow's wonderful, new Audio Center. MARKEL HIGH FIDELITY FANS-You are most interested in how well equipment sounds rather than what makes it so. You'll find Audio Center's Duplex Demonstration Studios a better and more modern place to hear what you want, under simulated home conditions and in complete privacy. Have all your questions answered by friendly experts. We welcome the opportunity of assisting you in the selection of the fine musical reproducing instrument you hope to enjoy for years to come. PILOT PRESTO R,J AUDIO ENGINEERS-You'll find your kind of personnel at Audio Center engineers who are efficient, courteous and helpful. Of. course,' Audio Center follows Arrow Electronics' tradition of having the largest stocks of everything in Audio at all times. PROFESSIONAL & INDUSTRIAL SOUND USERS-Audio Center is your Sound Headquarters because all your sound needs can be supplied with ultra-fast service at unbeatable prices. You'll save more, and make more, when Audio Center serves you. Visit Arrow Audio Center at the Audio Fair Come to Room 650 for valuable Audio souvenir. , , AUDIO ENGINEERING • OCTOBE R; 1952 65 FEEDBACK [contim(.ed from pa.ge 25J be 20.0 volts as indicated so that the drive E y will have a net value of 5.0 volts. T he plate circuit has a loss of 5.0 volts; therefore. the output Eo will be - -1- 5.0 I volts as in F ig. 2. The over-all gain is 45 . 0 ) - ~ 04°6db (35 ) 20 log ( 20.0 - f..) . T he loss due to feedback is equal to th e Q'a in without feedback, 20.0 db, minus th e i ain from (35) or 12.9564 db. This is not the amount by which noise and dis tortion are reduced, however, since the additional plate loss of 0.9 151 db does not contribute to this cause. T he feed back factor for the two paths is 1- A J {,- A zK 2 , and substituting we have 100- (- 100) (0.10 1-(-10.0 )(0.70 ) = 1.00- (- 1.00 )- (- 2.00 ) =4.00, equivalent to 12.04 13 db. F or purposes of computation, assume that this amplifi er without feedback would generate 10 per cent of second harmonics and has a noise level of - 40 db. The noise and distortion plate circuit voltages without feedback will be (- 50.0)(0.10) = - 5.0 volts distort i.o n and (0.01) (- 50.0 ) = - 0.50 volts nO ise since - 40 db is equivalent to .0 1. Feed back will improve the noise by 12.04 db while the distortion will be reduced by the factor 4.0. T he noise voltage, also las reduced by one-fourth, is - 0.125 volts atA with feedback. The two B circuits will feed back 0.30 of this voltage or - 0.0375' 11la.tl sf~OM"Otlf.tln volts. This noise voltage has nothing to V Radio and cancel it in the grid circuit so is re t\. t. \ . ~1 t. 0 amplified by the gain - 10.0 and produces ~ NO. I Military, T I~ tions Industria, . App .ca ;q.Ep = A(nEc+ nEr) (36 ) For Electron.c =- 10.0 (- 0.0375 ) other = 0.375 volts. T his voltage is out of pha e with the original noise voltage of - 0.500 volts so will cancel all but - 0.125 volts. T he ne\\' hum level is - 50.0 ) 20 10g ( - 0.125 = (37) Stancor is, of course, one of the world's largest producers of special design transformers for use in 20(2.60206 ) =- 52.0402 db all types of electronic equipment. which checks the theol'Y since the orig i nal noi se plus the improvement equals In addition, Stancor has the most complete stock the above value. line in the industry for u.se in your prototypes or lab The distortion voltage reduction fol equipment. If you need one Qr a hundred transform lows the same pattern ; the voltage fed ers in a hurry, you can probably find the type you back will be (- 1.25) (0.30) = - 0.3 75 need in the Stancor catalogued line. They are quickly volts, which when ampli fied is available through the Stancor p~r ts distributor in dEp=A( dEc+ dEt ) (38) your locality. =- 10.0 (- 0.375 ) = 3.75 volts. The new 24 page Stancor catalog lists 475 trans This feedback voltage added to the dis former and related components. Ask your Stancor JUST PUBLISHED ! tortion being generated continuously will distributor for a FREE copy, or write' us directly. reduce the modulation by-products by the amount of "gain" change in the input circuit. STANDARD TRANSFORME R C O RP O RAT I O N The author hopes that this paper will aid other engineers to obtain a clearer 3 5 6 8 E L S TON A V E N U E, CHI C AGO 1 8, ILL I N 0 I S conception of feedback principles, there by expanding the fi eld of uses to which ..... "'~~'--' - ... -'I both positive and negative fe edback may """- >Wi• .•• J be appli ed. 66 . AUDIO ENGINEERING • OCTOBER, 1952 THE VIOLIN [from pa.ge 35 ] are th e i-shaped openings in the belly that are presumably there to let the ' sound out. They appear to act like the ports in a reflex baffle, or as the in ertia component which together with the air in the body of the violin form a Helmholtz resonator. The following comments are made re garding them . by reference (2): If they are cut in the back of the violin, the tone is muted. If they are too small, the sound (resonant frequency) of the con tain ec.l ai r. is ' lowered ; if too large, the sound is raised. If they are too large or too near one another, the violin becomes harsh and shrill; if too small or too far apart, the tone becomes more wooly. Although one is tempted to dismi ss these observations as being inconse quential, we must not forget that in a musical in strument second-, third-, and even fO Ul·th-order effects may be impor tant, and perhaps the changes in the position and size of the i-holes may be of importance. TOMORROW'S AUDIO On the other hand, llluch nonsense has been written by well-meaning and naive violin makers about all these fac tors, and we must be on our guard as to what is merely their opinions and what is experimentally true. Expel'i ments indicate, for examp l e~ that above the air-body resonance, the belly is the principal radiating surface. In vibrat ing, its nodes are not necessarily at its edges ; instead, they m ~y be within its · surface, and the edges and sides of the AII-Triode Amplifier body may vibrate with amplitude. AND The body has to be fitted with a neck and scroll of maple, and ta il piece, fin gerboard, nut, pegs, and even chin rest Master Audio Control of ebony or rosewood. It also must be varnished, and here we come to more • THE FISHER Laboratory Standard Amplifier is, beyond a controver y and pseudo-scientific argu- shadow of a doubt, th e world's finest all-triode amplifier - and yet 'moderately priced. FEATURES I N BRIEF: High output -less than . ments than were presented by the al .3% harmonic di stortion at 40 watts (,08% at 10 watts.) lntermodula chemists of old. tion distortion below 8/10% at 40 watts. Uniform response within It appears that the varnish of the old .1 db, 20-20,000 cycles; 1 db, 5 to 100,000 cycles. Hum and noise Cremona masters has never been dupli better than 92 db below full output. Quality components, beautiful cated, and arguments have waxed hot workmanship . • THE FISHER Master Audio Control can be used and fu rious as to whether they used a with any amplifier. In'termodulation distortion is virtually unmeasur spirit or oil varnish. This is considered able; complete, profess ional phonograph equalization settings and tone more than a mere academic argument, controls; genuine F-M loudness control; 5 inputs and 5 independent fo r the varnish is considered to add con input level controls; cathode fo ll ower outputs. Self-powered. siderably to the tone of the violin. Write for illustrated brochure and fU ll specifications. 1'here has recently appeared an ar ti cle (4) that indicates that in the manu FISHER RADIO CORPORATION· 39 E. 47th ST., N.Y. facture of the varnish, metal rosinates were introduced that fortunately added to the qU fl lity of the varnish. Rosin was dis solved in potash lye, and then alum and coppers (ferrous sulphate) added to precipitate out the corresponding rosin ate. These were then dissolved in tur pentine and linseed oil added to form the varnish. To what extent, if any, the varnish affects the tone is hard to say; one has the feeling that emotion rather than I'eason sirays the luthiel' in this re spect. The old Cremona varnish, how ever, is a beautiful, lustrous coating that has withstood in remarkable fashion the ravages of time. (To b.e concillde'd) AUDIO ENGINEERING • OCTOBER, 1952 67 PATENTS [continued train page 4] vo ltage from the i. L amplifier. The tuned circuits are resonanted at the intermediate freq uency. The center point of each tuned circuit is connected to one element of a diode; the two diodes would most con veniently be in a single envelope, such as a 6H6 or 6ALS. R" probably with a reason ably high res istance value to avoid loading c" rnereiy' furnishes a d.c. path to ground for the cathode of V. If the signal input to the discriminator is at the exact frequency to which both cir cuits are tuned, the impedarlce of LJ and C, are identical as are those of L J and C,. The voltages at the midpoints of these tuned circuits' are identical, and the equal and .opposite diode currents create no voltage at the centertap of mixer resistor N, and acr-oss load resistor R ::. If the frequency of the input is higher than that to which the discriminator is tuned the vol tage at the midpoint of L,-c, decreases and that at the midpoint of L,-C. in creases due to th e transpositi on of the L's and Cs in the two circuits with respect to ground. The diode currents are then unequal and a voltage app ears between the midpoint of RJ and ground of a given polarity and an amplitude depending, over a limited fre quency range, on the deviation. If the input freq uency is too low, similar but opposite action takes place. The midpoint of R, is connected to a contr-ol tube-perhaps a reactance tube or simply an electrode of the Use with Your Own Audio Amplifier, local oscillator if it is of a type that can be made frequency-sensitive in that way-so Radio or Radio-Phono Combination, that the d.c. voltage output of the dis criminator tends to correct the oscillator or with new tapeMaster Model ' frequency in such a direction as to bring the intermediate frequency back to the SA-13 Power Amplifier and Speaker. ri i!'ht valu e. For the first time, a completely-flexible pro (A) and (B) of Fig. 4 shows the un fessional quality tape recorder like this-at usual range of control of this di scriminator. MODEL SA-13 The us'ual discriminator develops an output sllch economical cost! Advanced engineering voltage linearly related to frequency devia and customized design make the tapeMaster POWER AMPLIFIER tion, but correction voltage drops off to a natural choice of recording enthusiasts AND SPEAKER practically nothing above and below a everywhere. Can be carried anywhere and rather small band right around center fre used with an existing audio amplifier 'or Portable companion to .the PT- quency. T he new circuit . remains linear 125 tape recorder. Combines a combined with the SA-13 to make a com special type speaker, new ampli over only a similarly small j)and. but the plete tape recorder and playback assembly fier design, and effective principle co rrection voltage remains at a hi gh value far superior to other more costly equipment. of baffling. Amplifier response for (theroretically) an infinitely wide range Ideal for home, school or commercial use. ± 1 db 30-15,000 cps. Peak out both above and below center frequency. put 8 watts. Has separate bass A copy of any patent specifi cation may be and treble control. 12 " x 9Y2 " Complete with 5" spool of plastic tape ang obtained for 25 1 from The Commissioner of x 18\12 " high. . . $1950 7" empty take-up spool, in sturdy carrying Net I"'r'ice . Patents, Washington 25, D. C. case covered with waterproof leatherette, less audio amplifier and microphone. Size: 12Yz" x 12" x 9Yz" high. . $99 . Net PrIce 50 Built to RTMA Standards. Dual Track-Manual Reversal. Dual Speed-7.S" and 3.75" sec . • Single Knob Instontaneous Speed Change. Fast Forward and Rewind. "A" Wind Tape. Direct R2 Threading of Tape • Push~Pull Supersonic Bios·Erase • Response 50-8000 cps. ± 3 db at 7 .5 and 50-5000 cps. at 3.75 .dnputs for Radio, Phono and Mike • Outputs for Audio Amplifler and Headphone • Full Monitoring • Neon Record level Indicator for 105-125 V 60 cycle AC (Also available for 110-220 V SO cycle AC) • Operates Vertically or Hor;,i zontolly. Send for FREE Bulletin 102-A To Frequency Control FOR CUSTOM INSTALLATIONS Fig. 3. Model TH-25 Dual Speed Tape Transport Mechanism with Model PA-l Matching Pre Amplifier and Push-Pull Super somc Bias-Erase Oscillator. Fully wired, ready to plug in. Without spool of tape, take-up spool and carryin.g case. $8850 Net Pnce. Export: Scheel International, Inc_ Units may also be purchased individually Chicago 18, US.A. • Cable: Harscheel (Prices Slightly Higher West and South) Fig. 4. 68 AUDIO ENGINEERING • OCTOBER, 1952 CODED SIGNALS [contimted from pa,ge 44J A printed instruction card on what to do in case of an enemy attack is put out by the American Hotel Association and was observed in a room in one of the country's most recently built modern hotels. This instruction card is headed "SIRENS, HORNS OR WHISTLES," and then follows with the instructions : " 1. Step outside of your room and close the door. 2. Immediately sit or li e n ea l~ corridor wall. 3. Await instr1.tctions." Await instructions from whom? From bell-hops or possibly chamber-maids ? Isn't this a pitiful direction for a public hotel which may house as many as sev eral thousand transient visitors-men, women, and children ? Another instruction card put out by a County Civil D efense and signed by the director states : "The Red Signal is a sustained warbling wail on ji1'e sirens, or intermittent blasts by fire horns or whistles, lasting about two or ,three min utes. This means an air raid within eight minutes. If this is th e nor111a,l fire -alarm in Y 01W community, rega'rd' it as an air raid s·ignal onby if )'01t hea,r similar signals at the same time f10 0m 1'leighbor ing areas." Need I say more? Since the introduction of the original 604 speaker in 1943 the STEREO,PHONIC Altec 604 "duplex" has been [co'nl'iwlted fr om pa,ge 281 known to all as 4he finest loudspeaker that mi crophone and speaker bridged an oss money can buy. Now, after years of con the two outer channels improves the per fo rmance in this respect, though none tinuing research, the new Altec 604C "duplex" is here of the combinati ons tried are as good as to set even higher standards for qudio reproduction ... for the three-channel layout. the 604C will faithfully reproduce tones from 30 Trial Attempts to 22,000 cycles and handle SO watts of peak power! Listen T here have been various attempts to co mbine the advantages of the dummy to the amazing Altec 604C soon. Your ears will agree it's the finest head microphone mounting with the use loudspeaker in the world. of loudspeakers, though so far without any outstanding success. From the point of view of microphone technique the 604C SPECIFICATIONS: dummy-head mounting has the g reat ad Power rating ...... 35 watts (50 watts peak) vantage of simplicity, two microphones Network impedance ...... 16 ohms in a common mount being no more diffi Maximum diameter ...... •... . 15K6 inches cult to handle than a single mi crophone. Maximum depth ...... l1Ya inches T he limitations appear when considera tion is give.n to the time differences Weight with network ...... 40 pounds whieh- result in seating positions off the room axis. Referring to Fig. 6 it will Don't forget to listen to these new mem be seen that at the mi crophone the posi bers of the "duplex" line, the 12" 601A ti on of a sound SOUl'ce is characterized and th ~ 15" 602A. They are designed by a time difference proportional to the especially for the home. path-length di fference, and this holds fOI' all positi ons on a line midway between th e loudspeakers. A t a point such as L 9356 Santa Monica Boulevard, well off the center line the original time Beverly Hills, California ell tierence a-b is completely swamped 161 Sixth Avenue, New York 13, New York by the time difference cod which is char acteri stic of the relative pos itions of the li stener and the loudspeakers, and has no relation to the position of the source. I t mig ht be expected that the stereo- ALL THREE SPEAKERS ARE GUARANTEED .TO REPRODUCE ALL OF THE TONES FROM 30 TO 22,000 CYCLES! AUDIO ENGINEERING • OCTOBER, 1952 69 phonic effect would not be quite so ob vious in position off the axis of the room and this is found to be t}1e case in practice. Fig'nre 7 is indicative of the area in which effective stereophony is obtained. Though this appears to be a fundamental weakness of all systems using close-spaced microphones, the ad vantages of simplicity in the mi crophone technique justifies further work on the system. Figl.tre 8 indicates the technique used in all the accuracy tests. A caUer held a horizontal stave marked off in each direction from the center, and stood a90ut 25 ft. from the subject under test. The subject wore a light head harness carrying a horizontal sighting rod which was visually lined up on the center zero 95 of the stave at the commencement of the NET test. The caUer took up a position on a $99 25-ft. radius fr0111 the blindfolded sub ject and read passages from a book un til the test subject indicated that he was "on target" at each position. A third assistant read off the error in position on the reader's stave, along the sighting rod on the subject's head. This pro cedure was repeated at ten different an gular positions with five different sub jects and the errors averaged. For the indoor tests the same group of observers , repeated the procedure in a small the ater, the listening position being 55 ft. from the caUer. The results of the first series of tests a re set out in Table I and it wiU be noted that accuracies of the order of 1 deg. can be achi eved both in tutJ If,(J.W _ doors and outdoors. A comparison with the errors made when attempting to align the eyes 011 the stave zero showed that the accuracy of visual alignment is The 2nd Audio Anthology not more than twce that of an aural Ready about November 1 ali gnment. This is surprising, as the ears No bigger, no better than the original Audio are rarely used fo r the purpose of posi Anthology-in fact, it's just the same size and a Features-' tion fixing, a duty left to the eyes. perfect companion to the most authoritative book • Amplifiers you now have on the subject of home music sys During the indoor tests the oppor tems. But it contains ali new mater'ial"--reprints of • Preamplifiers tunity was taken to check the effect of frequencY-l'ange restriction on the ac over forty of the valuable articles which have most • Tone Controls interested )E's readers during the past two and a curacy of location. The results also serve half yeans. • Phonograph Equipment to indicate the information carried bv Advance orders a re now being accepted-so • Loudspeakers the various regions of the frequency make sure that you get your copy from the first spectrum. The technique remained· as in printing. The board-cover edition will be printed i'1 • Speaker Enclosures the previous tests but the source was re only a sufficient quantity to fill the advance orders • Tape Recorder Amplifiers placed by a hi gh-quality loudspeaker re -after that, only the paper-covered edition w il l producing speech picked up by a micro be available. Customary discounts to distributors. phone in another studio. Three filters having the characteristics shown in Fig . Board Cover $3.00 Paper Cover . $2.00 9 were used to define the frequency ------CUT OUT-MAIL TODAY------· range in the three tests, the re ults be Book Division, ing shOlvn in Table II. It will be seen that the majority of information on Radio Magazines, Inc .• source position is carried by the fre P. 0, Box 629, Mineola, N. Y. quency components above 500 cps Sirs : Enclosed is my D check D money order for . . .. , ... copies of the though the ear can find adequate infor 2nd Audio Anthology, mation ill the small amount of energy that remains in the region above 3000 (Please check one) D Board Cover D Paper Cover cps or below 500 cps. With the male speakel's employed in these tests, speech Name (print carefully) ...... , ...... , ...... inteUi gibility was zero when the band below 500 cps or the band above 3000 Address ... . . , ...... , . . ,' ,., . " . ... , . . .. . cps was being used. In tests we have noted that dyn'amic City ...... , ...... , . . . Zone . . . . . State ...... , . ... . locali zation (the locali zation of a mov ing sound source) appears to be appreci- 70 AUDIO ENGINEERING • OCTOBER, 1952 ably more accurate than the locali zation of a stationary source. The final point to be considered is the "vweight or hea"vweight technique to be used in obtaining two or three channels between studio and reproducer, probably the most difficult I problem of all. For X -in. magnetic tape, t\·\-O solution s a re fai rly straightfo rwal-d, the fir st being the use of two or three separate tracks on the same tape. Double track tapes are currefltly available and can be used for a two-channel system \\'ithout difficulty. Three tracks each .05 in. wide are 'possible, though agree ment will have to be reached on th.e relative position of the three tracks, as it is probably impossible to mount three recording or scanning heads side by side. Earl ier it was noted that two chan nels 6,000 cps wide, or three channels 4,000 cps wide, gave results which were subjectively assessed as being equal or better than a monaural channel 15,000 cps wide, and in consequence it becomes necessary to consider how best to use a medium such as tape which can deal. with a frequency band perhaps 20,000 to 25,000 cps wide. Nothing is to be gained by reproducing frequencies above 15,000 cps, and a more pleasing result can certainly be obtained by divid ing the band into two or three sepal-ate channels each 6000 or 7000 cps wide and using them for a stereophonic system. builds the world's toughest transformers P honograph records present a more difficult problem and as they may be in a complete range for every need superseded by tape it may never be necessary to solve that problem, but one From "flyweight" High Q Chokes to "heavyweight" Mod ulation bruisers, neat solution due to A. D. Blumlein of CHICAGO "Sealed-in-Steel" transformers are really rugged. Talk about E 111 I is worth noting. Blumlein pro "torture" -these units can "take it," a nd deliver complete dependa bility poses to record a two-channel stereo and continuous service under the most adverse conditions. Your elec phonic signal on an ordinary disc by tronic parts distributor can supply the complete range of CHICAGO N ew simultaneously using lateral and verti cal Equipment units for every modern circuit requirement: Power, Bias, modulation of the single groove. Equip Filament, Filter, Audio, MIL-T-27, Stepdown, etc.-all in exclusive ment was built and succesfully demon "Sealed-in-Steel" constr4ction. strated that this was possible. E M I have demonstrated 78 r.p.m. recordings Available in 3 Versatile flat to 20,000 cps and these would, permit ': THERE'S NOTHING TOUGHER Co structions two or three channels 6000 to 9000 cps THAN THE "SEALED-IN-STEEL" H-TYPE wide as suggested for tape. NEW EQUIPMENT LINE Hermetic sealing meets Broadcast-band AM radio poses on all MIL-T-27 specs. Steel even more di fficult problem, particu base cover is deep-seal so ldered into case. Ter larly in Europe whel- e all stations are on CHICAGO'S one-piece drawn-steel cases are minals her meticall.v a nominal spacing of 9 kc. Single side the strongest, toughest, b est-looking sealed. Ceramic bush ings . band transmi ss ion of two channels is transformer construction availa ble. The Stud-mounted unit. possible as the data in T able II shows one-piece seamless design (in a choice of 3 mountings) enclosing a n e lectronically that frequencies below 500 cps are of no p erfect unit, provides the best possible gl-eat importance to the stereophonic electrostatic a nd magnetic shielding, with Steel base cover fitted effect, permitting a double-sideband complete protection a gainst adverse atmos wi th phenolic terminal transmission of frequencies up to this pheric conditions. Whether your t rans board. Convenient num bered solder lug termi point, with single-sideband transmission formers must p ass the most r igid MIL-T- 27 specs, or are intended simply for average nals. Flange-mounte d . of the left and right signals on the upper applications-play safe-choose CHICAGO and lower sidebands, a shown in Fig. " Sealed-in-Steel" transformers. 10. On short waves there is no technical (-TYPE Wi th 10" col o r-c od ed difficulty. The audio bandwidth of a You'll want the full details on leads brought out through short-wave transmitter is sufficient to CHlCAGO'S New Equipment Line fi bre board bose cover. covering the full range of "Sealed-in L ead ends are stripped provide two or three channels as sug Steel" transformers designed fo r and tinn ed for easy so l gested for magnetic tape, or the carrier e very modern circuit a pplica tion. dering. Flange-mounted. Write for your Free copy of this im Il15lY be simultaneously modul ated by FM portant catalog today, or get it from and AM signals to give two channels. your electronic parts distributor. The renewed interest that has been shown both in Europe and A merica in the problems of stereophony indicates that it will be the next major step to wards obtaining a perfect reproduction. Under the stress of competition from TV, stereophonic sound may appear fil-st in sound movies and may be accompanied AUDIO ENGINEERING • OCTOBER, 1952 71 I 1 by the in troduction of a wider screen to TAKES THE "PORTERING' take advantage of the new freedom. OUT OF PORTABLE RECORDING CARRIER THE * DOUBLE SIDEBAND TRANSMISSION OF 'Battery-Operated Spring-Motor LOW ER AUDIO FREOUENCY PORTABLE TAPE RECORDER Fig. 10. Radio bandwidth usage fo r stereophonic transmission on AM. Field recording can now be made with as little effort as studio or home recording. Light and compact, the TABLE I tiny Magnemite is the first completely portable tape Comparison of the Accuracy of Loca tion i:1 Indoor and Outdoor Environments Size : ll Jf2 II 8 V2 x recorder! Earphone monitoring and playback facili 5 V2 in. ties built in. Powered by self-contained dry flash So u nd Source-Original Male Speech light batteries that last 100 operating hours. Four • Mean Error Stand ard Weigh :, i ncluding models are available for any speech or music Deviation batterie,s: 10 Ibs. I ndoors at a spacing recording requirement, including a model designed of 55 feet 1.04 deg . 1.15 deg. • Outdoors at a spacing Net, Price: $225 to NAB recording standards. "' Trade Ma rk Reg. of 25 feet 1.2 2.7 ii! W rite for co'mplete litera t ure, speci f i cation s and di rect factory p r ices TABLE II Accuracy o,f· Locati.on using Ba nds of AMPLIFIER CORP. of AMERICA· 398-2 Broadway· New Vork 13, NoV: Fi ltered Male Speech Frequency Std. Ra nge Avg. Error Deviation 50-500 cps 3.8 deg. 3.55 deg. 500-3000 0.9 3.8 3000-7J OO 0.5 3.4 ONLY 13 6 COPIES LEFT 50,-7000 0.7 4.7 REFERENCES $1.00 $.50 $.35 $ .35 1. \ "1. E . Kock, "Binaural localization and 1949 1950 195 1 1952 masking," 1. AcoHs. S oc. A m.. -ov. 1950. o June o August o March o March D etails o f an experim enta l d e t e r mitl a ti ~n of t he amount of discrimination against noise t hat is o September o April o May g iven by our bina ural hearing s ystem. o December o May 2. H arvey Fletcher, "H earing. the deter mining factor in 'high-fidelity transmi s June .... o sion." Proc. 1.R.E., J une 1942 . October An excellent paper which reviews m ost of t he ·'·:--,,'f o iactors known t ~ be of importance in obtaininig a hig h· fid eli ty ]'eproduct ion. T his paper is im AUDIO ENGINEERING, P. O. Box 629, Mineola, N. Y. portcmt t f") anyone int erested in the st1bject o f hig h·fide lity. I enclose ...... Send issues checked 3. Galombos and Davies, "The response of single auditory fibres to acoustic sti mu Name ...... lation." 1. N ell1'o physi% gy, 1943, No.6. Describes nerve voltage measurements that Address ...... appear to h a ve an important bearing on the mech anism o f t he stereoph onic effect. ~{ os t in City ...... State ...... •...... teresting reading . 4. F . M . Weiner, "Difhaction of a sound wave by the human head." 1. Aco'/ls. Soc. A 'IIl,., Jan. 1947. 5. J . c. Steinberg and W . B. Snow, "Au ditory pel-s lX!c tive physical factors." Eta. Eng., Jan. -1934. o Il e 01 a grou p of six pa pers devoted to s~ereo phon y. That lo udness d ifferen ce is the m ain factor in bin aura l locali zation i ~ no t no w so widely beli eved as in 1934, but t he group of papers is required reading. 6. ]. Moir, "Stereophoni c sound," W ire less World, March, 1951. 7. J . Moir and J . A. Leslie, "The stereo phonic reproduction of speech and mu sic." 1. Brit. I .R.E., 1951 Radio Con vention. 8. K . de Boer, "Stereo ph ollo'ic SOlU ld repro du ction," Philips Tech. Re\, .. Apr il, 1940. ' A n account of the factors that are o f im portance. 72 AUDIO ENGINEERING • OCTO BER , ~ 9 52 • AUDIO ENGINEERING subsc ribers can receive, without cost or obligation, a complete 128 page catalog section on T est Equipment and Instruments, as reprinted from the 1200 page RADIO'S MASTER, the Industry's Offi cial Buying Guide. This section catalogs in detail the products of the leading Instrument and T est Equipment manufactur6rs - all in 1 handy booklet. It is complete with descriptions, specifica· tions and illuti trations as written by cach manufacturer. You will find this largc catalog section extremely helpful and a handy reference. This FREE offer is made potiti iblc by a special arrangement between AUDIO ENGINEERING MAGAZINE and the publishers of RADIO'S MASTER. Be snre to get your ('opy ... just mail conpon NOW. AUDIO ENGINEERING MAGAZINE P. O. BOX 629, MINEOLA, N. Y. Please send, without cost or obligation, the 128 page Instru These manufacturers do not catalog test equipment In Radio's Master. Separate ment and T est Equipment Catalog as reprinted from Radio'~ catalog sheets will accompany each Master. booklet. Nalne...... __ .... _...... -...... Audio Instruments Corp. Ballantine laboratories Addresb ...... ____ ...... _. .. _...... -...... General Radio Corp. Heath Company . City...... __ ._. _Zone. _...... Sta te...... '" ...... - Hewlett-Packard Corp. AUDtO ENGINEERING • OCTOBER, 1952 73 • So much for jacks 1, 2, and 3. Jacks RADIO STUDIO 4 and 5 are the turntable output jacks and their tip pairs must also !'Un down [cont-inu,ed from page 31] the rack in cable B to the 'same low level terminal block # 1. These pairs a re Run ni ng Sheets numbered 4 and 5 and are assigned to The next step-is to put down on paper block terminals 7 and 8, and 9 and 10. the detailed wi ring information 'needed The normals of these jacks are shown to show the wireman the exact starting as wired to the normals of preamplifier and stopping points of each rack pair, input jacks 16 and 17 respectively. and the connections required for their The next two jacks in numerical shields. It's generall y a good idea to order, jacks 6 and 7, turn out to be as start with the jack fie ld- specifically signed to the tape recorder microphone the low-l evel jacks- since the jacks are (inadvertently omitted from the block the most common point for all the ele diagram ) and the monitor head output. ments of the rack. Start with jack # 1 S ince the 1'ack cabling layout shows that and proceed in numerical order of jacks. the tape recorder is ab'ove the jack fi eld, A useful form fo r systematizing these the tip pa irs from these two jacks must ; The new. AlliED catalGg is your best data is the running sheet of Fig. 4 in obviously run in another low-level cable ' buying gui de to the wodd's largest, which is shown a portion of the lo-w running j·tP the rack from the field. These latest and most complete selection level data of the small audition studio jacks are thel'efore omitted from the run of audio equipment. All important used for illustration -in this series. The sheets of the down-running cable Band high-fidelity lines are .featured. form is self-explanatory except perhaps we proceed with the remaining low-level jacks shown by the block diagram as All equipment, including professional for the check columns, Since the run ning sheets are checked and rechecked wired to the terminal block or to other ',:,_ , qu~lity cOll)ponents, is available from against the interconnection sheets, block components located below the jack fiel d. stock. Whatever your needs, you can diagram, etc" by both the designer and A check against omitting any pairs is i count on ALLI ED for quick, the wireman, the numerous check marks obtained by comparing the number of tend to obscure th e data. This is a seri pairs listed on the run sheet with the ous source of error when the typist later total shown on the previously prepared retypes them fo r permanent record, and cable list. As soon as the wiring data IS avoided by providing' columns fo r the is entered on the running sheet for each check marks, jack, that jack is checked off the jack I t will be noted from the block dia fi eld layout rather than the much-abused g ram that the tip pairs from jacks I, 2, block diagram (since the latter may not and 3 go to microphones. Since these show every jack ). In like manner, the are outside the rack, the pairs must be low-level jacks whose tip (or normal ) wired to the low-level terminal block. pairs are shown by the block diagram as Ref,erence to the rack cabling layout going to rack components located above (Hg. 3 of the preceding installment) the jack field are assig ned pair numbers shows that the only 100oV -Ievel cable run in the up-running cable A and are en ning down the rack to block # 1 is cable tered on another set of running sheets. B. The running sheets are therefore This system results in each set of run started as shown in F£g, 4. The jack ning sheets applying only to one cable, numbers are listed in the EQUIPMENT which facilitates future reference. The column of the F ROM g roup, the jack ter running sheets should also sho\\; whether mll1 al numbers going under the T ER the shield of each pair is grounded to , M I N AL column. T he two tip terminals the jack frame or to a gl'ound bus lo of each doubl e jack are numbered 1 and cated on or near the terminal block, or 2, the normals being 3 and 4. S ince the to an amplifier chassis. This can be in tip pa irs for microphone jacks 1, 2 and 3 dicated by any convenient symbol, such aI'e all in cable B, they are numbered as an "x" placed in the appropriate TER 1, 2, and 3 respectively in the pair col MINAL column of the F ROM or TO group, umn. At the other end, these pairs are with perhaps a note at the top of the assigned to t e r~nin a l s 1 and 2, 3 and 4, 5 sheet to identify the symbol. and 6 on termll1al block # 1, these data The running sheets (and the intel' • Com plete home music systems being entered in the columns of the T O connection sheets when you come to • All famous-make am plif iers g roup on the run sheet. them) should refer by number to any • Hundreds of speakers and It's a good idea to show the connec separate sketches which may be required enclosures ti ons fo r the normal terminals of the for clarity-for example, when pai rs > • Widest selection of tuners jacks (and any multiples ) on the same split in series connections with other • Everything In phono run sheets as the tip connecti'ons, as this pa irs, or go to rack components lacking components keeps all the jack wiring information clearly-identified terminals. It is impor • Talil& and d isc recorders together. The block diagram shows that tant to list the sketch in its column _. Fullest microplione listings the normals of jacks 1, 2, and 3 are (Fig. 4) when the running sheets are wi red to the normals of the preampli fi er being made up, because that's the ti me input jacks 13, 14 and 15 respectively, you are most conscious of the need for If it's anything in AUD IO- and this information is recorded on the the sketch. Then the sketch number, a It's available at ALLIED ! running sheet on the line below the tip short descriptive title and the jack and information for each jack. W hile the pair numbers involved, should be en fo regoing description is based on con tered immediately on a sketch register SEND FOR ventional double jacks, the !'Un sheet which serves as a guide to the drafts FREE CATALOG wo uld be no di ffe rent fo r single jacks as man. This provides reasonably good in in any case there would be the equiva surance that preparation of the sketch ALLIE D RADI,O CORp. lent of two tip terminals (actually one will not be overlooked until the wire tip and one ring terminal fo r single man is loudly proclaiming that he can 833 W. Jackson Blvd., Dept. 17-K-lo Chicago 7, III. jacks) alld two normal terminals. not go on without it. 74 AUDIO ENGINEERING • OCTOBER, 1952 Aftel' all the jacks have been shown on the running sheets, othel' rack com ponents havi,ng terminals should be Westre'x "Di'stributes listed, such as amplifiers, equalizers, tuners. etc. It is obvious that after a while, the running sheets will be call ing for pairs that have already been accounted for by the earlier jack-field entries. For instance, by the time the input terminals of preamplifier #6 are 3SMM FULL WIDTH ( OATED 3SMM PROFESSIONAL MAGNA·STR IPE * listed under the FROM g roup as wired to the tips of jack 18, the pa ir in ques tion will already have been assigned a number when the terminals of this sa:me jack were listed earlier under the FROM 16MM FULL WIDTH (OATED (Single Perforated) 16MM FULL WIDTH COATED (Double Perforated ) g roup. In such cases, an asterisk 011 the appropriate line ' of the runni ng sheets will indicate to the wireman that this pair has already been r un . So much for the running sheets for 17'f,MM FULL WIDTH COATED 16MM MAGNA· STRIPE * the rack. Stock consoles Heed no run n i ng sheets since thei r internal · com ponents are already wi red to the con sole terminal blocks. However, in MAGNETIC TAPE custom-built consoles constructed by the station staff, the va rious internal connections to the blocks from mixers, switches, output transformers, etc., must be prescribed on running sheets in Reeves Magnetic Film and Tape, Feat,uring ••• much the same manner as for racks, ex cept that console sheets sta rt with the • ECONOMY of low firs t cost and lo ng life. • LONG STORAGE LIFE ass ured by use of new I ri ' aceta te sa fety film base. console terminal blocks in stead of the • CONS TANT OU TPUT assu re d by e lectro nicall y co n troll ed cooting. • OXID E FLA KING or rubbing o ff g reatly red uce d du e rack jack fi eld. to high adhe re nce of magnetic coating. • GR EATE R DY NAMIC RANGE beca use of high ly uni, • MEC HANICAL U N IFO~MITY a chieved by a special Rack W iring Practices form oxide dispersion. coating formu la that minimizes curl ing . Before discussing the interconnecti on • H IGH FREQUENCY RESPONSE co nfarms to ind ustry • 35MM FILM EDGE NUMBERED every foot i n opposi te standards. sheets, it might be well to consider a directio ns a s a n aid in editing . • POLI SHED SURFACE red uces mechanical squeal. • CUSTOMER S REClAIMED CLEAR BASE ACETATE FI LM few points in regard to the actual wi r can be stri ped wi th a mag netic coating - on ing of the racks from the running HIGH OUTPUT be ca use o xide dispe rsio n is engineer added econo my mea sure . ed for ma xim um sensitivity. sheets. Ordinarily, the low-, medium-, • DEVELOPED OR UNDEVELOPED PHOTOGRAPH I C FI LM and zero-level cables a re run up and • LO NG HE AD LIFE res ults from coati ng oxide par can a lso be coate d for te levision prod uct ions or ticles with low-fri ction materia l. othe r simil a r usa ges. down the rig ht side of the rack as seen from the rear, and the high-level and Westrex now distributes Reeves Soundcraft full -coated mag po wer circuits are run on the left side, Spacing between cables of different netic recording film , "Magna-Stripe*", and magnetic tape in level groups should be a minimum of li ne w ith its policy of providing studios with the fi nest record three inches between edges ; more is ing equipment and accessories. often desirable. Before any cables al'e ~ T rade m a r k of Reeves So u ndcraft connected to the jack fie ld, it's a o'ood idea to put in the normal and multiple Research, Distribution and Service for the Motion Picture Industry connections, It is difficult to accom plish this rather close work between jacks after their terminals are largely /~~ obscured by incoming pail'S. Cables Westrex Corporation ® WestreX I running between the terminal blocks '\ ..../ 111 EIGHTH AVENUE, NEW YORK 11 , N. Y. and the jack fi eld a re best begun by HOllYWOOD DIVISION 6601 ROMAINE ST!(:EET, HOLLY WOOD 38, CAL soldering the various pairs to the tel' minal block while the lattel' is still on the bench. This eases the 10nO' and ti l' ing job of working on the block after it is installed in the bottom of the rack. but incoming interconnection p ain~ must still be install ed the hard way. FAIRCHILD RECORDING EQUIPMENT CORPORATION The cable can then be formed in place and run up the side of the l'ack to the jack fi eld which is usuall y at a CJ n Synchronous Disc Recording & Playback Units venient working height, ( Fign?'e l A of the preceCling install ment ), Cables run are available from ning across and behind the jack field can if necessary be supported by and lashed to a stiff wire stretched across the rack. Always . include spare pairs in the rack cables and keep a list of the num • ~~~~~ c~p~!~~O ' bers of the spare pairs in each cable. 730 Fifth Avenue, New York 19, N, Y. • PLaza 7-3091 T hey come in handy for omitted cir Exhibiting at the Audio Fair - Rooms 6 J 4 & 6 J 5 cuits and as substitutes for broken or AUDIO ENGINEERING • OCTOBER, 1952 75 shorted pairs. T heil- ends can be coiled have several cables of a g iven level up at the jack fi eld and at the terminal g roup coming off the same block and Presenting _ block. Be sure to number all pairs ~ n a ll these cables will a ppear on the in cluding spares, at both ends, selecting terconnection sheets, and not neces the label location where it can be visi sarily in numet'ical order of pair num ble after the pair is soldered in place. bers. T he label should show cable letter and Occasional1 y, in more complex in pair number, thus : B 12_ P rinted ad stallations, cables rW1l1 ing between hesive labels used by elec tricians and widely separated points sometimes in known as "Quik-Labels" are available for this purpose. This type of label also cl ude pairs which run benveen inter comes in handy for numbel-ing all jacks mediate points and are numbered as LOUDSPEAKERS with numerals vis; ible from the rear, as pairs of the " parent" cable. For ex in th e a convenience to the wireman. ample, if there were six adjacent racks lux urious setting Since polari ty is important in speech numbered 1 through 6 the cable car rying zero-level pai rs between outer of in put systems. be careful to pole all jacks and other components consist most racks 1 and 6 could also carry ARROW ently. This can be done almost auto zero-level pairs between racks 3 and 5. ELECTRONICS' matica l1 y by adopting a color code. F or In such instances, the composition of example, the red member of the pa ir the cable is not completely described by can go to the right tip terminal of each the number of pairs it caIT ies away double jack, and bl ack to the left tip. from the block of rack 1. To avoid The same rule woul d apply to the nor overlooking the other pail-s when fi g d esigned to mal conn ecti ons. F or single jacks, red uring conduit size or installing the COMPLETELY could go to ti p and black to ring. At cable, it is necessary to refer to the in d emonstr ate the tenllillal blocks, red may be as terconnection cable layout sketch where SOUND signed to odd-numb ered terminals and these turn-offs and their quantities black to even. Similar conventions ap should be shown. When there are many in its n atural ply to terminals of mi crophone and such turn-offs, the sketch becomes clut _ setting turntable wall receptacles. tered and it is helpful to keep a cable make-up sheet for each " pa rent" cable, UNIVERSITY Interconnection Sheets li sting the starting and terminating LOUDSPEAKERS, As the rack cabli ng layout was the points fo r every pair in the cable. INC. basis fo r the running sheets, so is the Construction Materials interconnection cable layout the basis 80 S. KENSICO AVENUE H aving the material on hand in WHITE PLAINS, NEW YORK for the interconnecti on or cross-con nection sheets_ This layout was shown proper quantities and to exactly the in Fig. 4 of the preceding installment right specifi cations before beginning and indicates all the cables and con constructi on can spell the difference duits leading from the rack to the con between a first-class and a mediocre in- sole, announce booth, etc. Preparation tallati on job. Listed below are the of the interconnection sheets (Fig. 5) principal construction materia ls, (ex should start with the terminal blocks clusive of audio equipment and acces CONGRATULATIONS as the most common point in the entire sories) need to install the plant. studio installation. T he terminal "b lock Greenfi eld conduit & Mike plugs & recep to numbers a re li sted in the EQUIPMENT fittings tacles ARROW column of the FROM group and the Wiremold conduit & Rubber-lined c a b I e numbers of their terminals are listed fittings clamps ELECTRONICS' in numeri cal order in the TERM INAL Assorted wire and Brady "Quik-labels" cable Cable shi eld termi na column. The equipment and the ter Terminal blocks ti ons minals to which they are to be con Assorted t e r min a 1 Nuts, bolts, washers, nected are listed in the columns of the strips wood screws TO g roup. T he interconnection sheet Jones plugs & sock Electrician's "Dux on creating picks up the rack internal low-level cir ets seal" a new cuits at the rack terminal block where Lacing co rd Spare tubes & fu ses the running sheet left them and carries Tests and Adjustments and them out to the console, turntables and othel- external destinati ons. It is im There is a great temptation, after inspiring portant that both the running sheets the last connection has been soldered. and the interconnecti on sheets proceed to turn on the power and play a rec way to in numerical order of terminal numbers ord to hear what it sounds like. While this may result in cheering up the chief demonstr ate of the vari ous terminal blocks as far as possible. As in the case of running " engineer- who by this time probably sheets, the interconnection sheets needs cheering up- there are other shoul d show shield c01ll1 ections by an things to be done first. There are two "x" in the appropriate column. T hose phases to the check-out process : one pai rs shown as running back on them is to check the mechanical and electri selves should be marked with an as cal condition of the cabling, and the terisk and should of course, bear the other is to test and adjust the system same pair numbers previously assigned. as a whole. BELL SOUND The same form is used fO I- both run It's a good idea to inspect the cables, SYSTEMS, INC. ning and interconnection sheets. As terminal blocks and the mechanical illustrated, both carry the pairs of only condi tion of the racks and console "' in 555 MARION ROAD one cable. This is deliberate for the g~n e r a l for obvious breaks, sagging cables, dirty terminal blocks, scraped COLUMBUS 7 , OHIO running sheet but is true of the inter connection sheet only because there is insul ation, etc. Then comes the tedious only one low-level cabl e in this par business of checking each pair for con ticular in stal1 ati on. Larger in sta l1 ations tinuity of each conductor, continuity 76 AUDIO ENGINEERING • OCTOBER, 1952 of the shield, shorts between conduc tors, shorts between conductors and shield, and polar ity. Part or all of this can of course be done by the contractor who installed the conduit. There are short-cuts such as checking circuit con tinuity and polarity from one end to the other, instead of hom jack to, block, block to receptacle, -e.tc. However such checks will not necessarily show up shol·ts to shield nor pl"Ove shield con tinuity. Neither will they disclose two polarity etTors in cascade- an impor tarit point ",·hen patching into intel' mediate elements of a circuit for emer gencies or special set-ups. Check grounding conductor continuity be Built to give years of service without change in . tween racks and other grounded frames calibut'ial'):', EveQ witbo.ut d eS1l·in'tOrs; K 'elt AUDIO .ENGINEERING • OCTOBER, · 1-952 77 noise, and distortion. Incidentally, it is well to have the oscillator distortion measured to make sure this value is not a ~ignificant factor in the over-all sys tem readings. Set the microphone gain, master gain, and monitor volume controls at normal operating position- possibly half open and feed into each input in turn' a 1000- cps signal which defl ects the console VU meter to zero with the meter attenuator knob set so that the net VU meter read ing is 10 db above desjred program peaks. T he load section of the gain set is then plugged successively into the output jacks of each amplifier between the console and the li miter to permit ad justment of thei r gain to the required value. The lim iter ampli fier is then aligned in accordance with the ma·nufac turer's instructions to provide the nece - sary gain at the threshold of limiting and to adjust the degree of limiting to the recommended amount- frequently 5 TYPE 4200 db. The gain settings of components be yond the li miter are then adjusted with the gain set. A standard VU meter could be used in place of the gain set provided the circuits it bridges are properly termi nated. After all gains have been adjusted, the frequency response of the over-all sys tem can be checked wi th the gain set and if the results a re below expectations, the response of each amplifier and other cir cuit components are checked individu all y. The same over-all and subsequent point-to-point check procedure is used for distortion at various frequencies, at the same 10 db-above-program level used for frequency-response measurements. Noise levels are detemlined by driving This unit has been developed to meet present day requirements the ampli fie r or system under test at for compactness. The filter requires only 3Y2 inches of rack space. 1000-cps with the gain controls in nor Features: mal operating position and calibrating • LOW HUM PICKUP through the use of toroid coils. The unit may be the noise-and-distortion meter in accord used in circuits having signal levels as low as -40 dbm without the ance with the manufacturer's instruc necessity for taking special precautions against hum pickup. tions. The 1000-cps signal is then re moved and the noise is read from the • LOW DISTORTION: The filter may be used at levels up to plus 20 dbm meter-scale, modified by any attenuator with negligible intermodulation distortion. settings on the instrument. Improper • RELIABILITY: All capacitors and inductors are hermetically sealed for grounding and impedance mismatches lifeti me service. Aging effects are negligible. are common causes of over-all noise, distortion, and POOI- response in systems General specifi cations: whose individual components may be DIMENSIONS: Standard rack panel, slotted, 3%" high. Maximum depth 7%". qui te satisfactory in these respects. CONTROLS: low frequency cutoff selector knob, "high freque ncy cutoff selector knob, The somewhat tedious gain-set method on-off key. of ~hecking response can be avoided by RANGES: Both low and high frequency cutoff controls cover 100, 250, 500, 1000, 2000, playing a sweep-frequency record such 3000, 4000 and 5000 cycles. as the C1arkstan # 1000A and 1000D on ATTENUATION: Approximately 16 db, per octave on both high and low " frequency cutoff the turntable and feeding the output of points. the amplifier being observed into a cali IMPEDANCE: 500/ 600 ohms,. in-out. brated oscilloscope. 2 This enables the re FINISH: Engraved panel fin is hed in medium gray baked e"namel. sponse over the entire spectrum to be (Spedal colors available upon request.) observed at a glance and also gives The filter has standard input and output "jacks located on qualitative indications of harmonic and the front panel in addition to the terminal block at the rear. intennodulation distortion and transient response. A check on stability of the over-all system can be made by boosting the level Send for Bulletin S another 10 db at various frequencies. This should cause no oscillation in a stable system and little or no change in 11423 VANOWEN STREET, NORTH HOllYWOOD, CALIFORNIA • SUnset 3·3860 freq uency l-esponse. And since the ear is Manufacturers of Toroid Inductors, Decad ~ Inductor. Inst ruments, . 2 Wayne R. Johnson, "Analyzing swee\> Wave Filters, Resistive Networks, and Precision Resistors frequency transcriptions" AUDIO ENGINEER Eastern Representative: Burlingame Associates, 103 lafayette Street, New York 13, New York ING, October, 1947. 78 AUDIO ENGINEERING • OCTOBER, 1952 the ultimate consumer of the station's audio merchandise, listen critically to live program material over the control room monitor speaker and to the play back of recordings made from the sys tem. Measurements may indicate every thing in good condition and yet the speaker output may not sound right. Speaker hangover, speaker location, im proper acoustics in studio and/ or con trol room, and poor transient response of one or more system elements are possible causes of this trouble. BACK COVER SPEAKER CAN and Conclusion PLASTER RING ASSEMBLY This completes the series of five arti cles on planning and building radio stu combined with dios. Incidentally, it's almost as much LOWELL SPEAKER BAFFLES werk to write about their construction as The lowell steel back cover speaker it is to build them. The writer would can and plaster ring assembly is like to express, belatedly, his thanks to used for recessed speakers in new' Mr. M. J . Kodaras of Johns Manville construction or remodeling for com for. his friendly assista.nce in the prepa plete protection of the speaker. ratIOn of some of the acoustical con struction material in Part 2. ' Steel back speaker can is made of 22 gauge steel, and a 22 gauge steel plaster ring, :::. with 90° spaced speaker baffle mounting holes, is spot welded to the can. Plastic roughing compound applied throughout inside of speaker can·, to prevent metallic PICKUP DESIGN resonance. Speaker leads can be brought into the assembly at any location. Furnished with %" knockouts on all sides, and all mounting hardware, including [continued from page 64] speed nuts. ward force can be obtained by deliber w/·ite for complete specifications and prices today! ately depa rting frol11 a level motor board, and so raising one side of it that LOWELL MANUFACTURING COMPANY the pickup wi ll be climbing "up hill" 3030 LACLEDE STATION ROAD. ST. LOUIS 17. MISSOURI very slightly as it plays through the r ec Canadian Representative: ord. By careful adjustment of the slope, the downhill force can be made to pro Atlas Radio Corp., 560 KING ST. W •• TORONTO. ONTARIO vide force C. Arm-bearing Friction A nother means of achieving the same result-and one employed by the writer in a pickup designed in 1939-is to in troduce deliberately a slight friction into the arm bearing. This method is only suitable fo r use with normal record-s which start at the outside. When plav ing such records, the head traverses tile record from the outside toward the cen ter. Any friction in the arm . bearing DEPENDABLE ••• COMPACT ••• EFFICIENT then resists that motion and so pro: vides an outwardly acting fo rce during operation. (@!l1aGlIf iE'~ p~ In moving-coil pickups which have Carter DC to AC Converters, Dynamotors, Genemotors, no iron in the moving parts, the exact Magmotors, and Inductor Alternators (invertersl are angular position of the coil is (within made in a wide variety of types and capaciHes adapt reason) not material from an electrical or magnetic point of view. Nor is there oble to communications, laboratory, and industrial ap any unstable magnetic effect tryin g to plications, of many kinds. Widely used in aircraft, marine, and mobile radio, geophysical instruments, laboratory work, ignition, timing and many other uses. (C Simple Test for Balance If anyone wishes to test whether the lateral forces in his own pickup are bal anced, a simple approximate method is to rest the stylus on the uncut edge of CONGRATULATIONS a record and all ow slight rotation of the to turntable. Prominent inward or outwarcl ARROW force wi ll then cause the pickup to sli de in the corresponding direction. ELECTRONICS' Since the inward force depends on the friction between the stvlus and the disc. this test is only appI~oximate, for the friction of the stylus' on the plane sur face may be different from that experi on creating enced when riding properly in the anew g roove. If the stylus has been used, it and may also have developed a shape causing it to "skate" in the preferred direction. inspiring The most certain test is to examine a way to used stylus (not diamond) under a mi demonstrate croscope and compare the wear on the two sides. T his gives information as to the average state of affairs under the actual working condi tions. (As a cau tion. remember that when turning points upside down and looking at them un del' news in years ' a microscope, one's ideas of direction can play funny tricks.) 'With an offset head, it is usually the in si de surface of the stylus which shows most wear. If so, ttl PEI!RlESS ' RECORDING DISCS the inward-acting resultant of A and B has not been countered sufficiently. The . Electri~al Products NATIONAL reader will now know what to do. \ HOLLYWOOD A DIVISION OF 1475 EL MIRADOR DRIVE See You at THE FAIR PASADENA 3, CALI·FORNIA HOTEL NEW YORKER Oct. 29, 30, 31, Nov. 1 9356 Santa Monica Blvd., Beverly Hills, Calif. 16t Sixth AVIl\.ue, New York t3, New Yark M.. ' •. .,. ,k BE THERE ':;C 0ii • 'C .i. .. ~ AUDIO ENGINEERING • OCTOBER , 1952 LONDON LETTERS [continued from, page 14] • Firs t Williamson Type Amplifier suppl ied with matching p r eamp l i fier • U ses Alt(:>c L ansing Pee rless output transformer. • Practically dis tortion less -Harmonic and in· termodulation dis tortion both less tha n l/ z of through two output channels, using 30-watt 10/0 at 5 watts output. amplifiers in each. • Frequency response + 1 db from 10 cycles to 100 kc. The Radio Show is organized by the • Output impe dance 4 , 8 , or 16 ohms. The n e w H cnthkit Wi lliamSon T y pe AmpJifi cr kit I s Radio Industry Council, ;which in actuality the h est o htainahle in amplific r .s t oday-lhe c hoi c ~ of the really d i s c<'l 'nin !~ lis tcnc r . Yo u en n h e ar the is composed of four trade associations : diffe r e nce ami m castlJ' C' m e nts a ctually bear o u t the f~~~~r~ 6 cg~ r~!nl~ ~('· 1 6ri"c~ ~l e:~I~ ~\~ "e~~~n~~ t e n/ t~~ 1. The Radio & Electronic Component hig h s and lo w s wi t h Cllua] ol" !s pncss ;lOd clarity. Harmo nic nnel inte nllodu lntion dis to rtion bo th less Manufact1,lrers Federation (Compo tha n 1fz of 1 % at 5 W:ltts output elimina t e the hars h lIml unplells ;lnt qUlIlities which contribute nents, measuring and testing instru to Ii s t c ni n~ f;Jti ~ u c. The circ uit is s imilnr t o the o ne publis hed in / ments, sound reproducing equipment, Audio E ng inee ring Mag;Jzine for Novem ber, 19 4 9 , a nd is con s i€i cl"C' d by e ng inecr s throug h out the etc.) a u rllo fi e ld 01 1; one o f t1 w \Jcst ever d e ve lo pe d. The Mnln J\ mplifi(,1" ( which n, ny b e p urc hased s epa - r;Jte ly) cons is t s o f a voltage amplifie r and phas e s plilfe l' us ing II 6SN7, n driver s inge u s ing a 2. Radio Communication and Electronic 6SN 7 . :\Ild a pus h -pull output s tage u s ing a pair Engineering Association (radio and o f 807 tuhcs. Thc outpuL tnms fo rme r is manufne- ture d by t he P cerless D ivis ion o f Allee L;lOs ing television transmitters, communication a nd is buill to thc ir hig h csL s tnnd:II"ds . Output impedances o f 4. S . nnd 16 o hms a re nv:.ll:.ble. The pow e r supply u s e s equipment, navigating aids, industrial 1I scpa rate chassis wHh hus ky Chic ago Trans forme r po w e r tr;lIls fo nner a nd c hoke . a nd 7 00V Mnllory filters fo r long electronics, etc.) hum-free o pe rlltl o n. A 5V<1 G r ectifie r is u sed. The m a in amplifi <.' l· and powe r s upply are cac h o n a c h:..,sis mcns lII'lng 7" hig h by {P h " w ide by 11" long. 3. British Radio Valve Manufacturers PREAM PLiFIER AND TONE CONTROL UNIT KIT The pl'c:lInpIIHe l' kit cons is t s of : a 12AX7 (or 12AY7) dUlIl Association (radio and television tl'io d (' (i1"R t ;unpllflcl' s tage with a tum-over contro l fo r LP o r 7 8 r ecord ty pes , and n 1 2 AU7 a mplifie r s t.age with In valves, cathode ray tubes, all types of divhJunl b nss .md treble tone contro ls whic h each prov ide electronic tubes) up to 1 litlh o f boos t or ntte n uatlon. A switc h on p anel sc leels eithe r mag n e Ue . crys ta l, o r tune r input ~ . Preamplifier :l1 s o Is weO s uiLed to c u s to m ins talla ti on s _ it w ill operate in eithe r "crtienl or h orizonta l pos ition, a nd s pecia l WA-At Amplifier kit - Combination 1- 4. British Radio Equi pment Manufac no tc hed shafts of the controls nnd s witche s a llo w a variety (Main Amplifier a nd Power Supply) com· of s hnrt le ng ths to be s e lected. Dime n s ions: 21/4" hig h by plete with WA-PI Preampli. turing Association (radio and televi 101/4" wide by 71/4" decp. sion receivers, sound reproducing ~ ~r l b~~t(Sh~~~~ ~~;rresiVo~tiy ) $69.50 equipment, etc.) WA-A 1 Amplifier kit only - Combin ation 4 - (Main Amplifier and Power SUpply). Le s s WA-PI Preamplifier. A tremendous variety of equipment was 7S~~~p~l~x~~s 02n~y~~;: ...... $49.75 shown at this year's Earl's Court Exhibi WA-PI Preamplifier Kit only. (less power tion, and included accumulator charging supply) (Tubes included). To· equipment, aerials and aerial equipment, ~",!p~~!~. o';'~~re~11~~·s :)~~~~~~~_~.. $19.75 amplifiers; batteries, battery chargers, cabi nets, cables, cameras, capacitors (fixed and variable), car radios, cathode ray tubes, chassis, chokes, coils, tuners, etc., coil wind ing machines, connectors, deaf aids, elec tro-medical equipment, fuses, gramaphone motors, needles, and pickups, headphones, industrial electronic apparatus, lenses, loudspeakers, magnets, measuring instru ments, microphones, plastics, public ad dress equipment, radar, radio phono combi nations, radio receivers, record changers, record playing units, recording equipment, rectifiers, resistors, service equipment, sockets, solders, suppressors, switches, tele vision receivers, testing equipment, time switches, tools, transformers, transmitters, valves (tubes), wholesale distributors, STYLUS PRESSURE CAN DO FOR wires and cables. W·202 or REP RO 0 U ClI ON FIDELITY AND Space does not permit the discussion of W·202·C RECORD LIFE????? any of these products in detail, but I have Cartridge noticed certain differences in emphasis be Set You con operote with' stylus pressures tween the present British market and our down to one gram with the new WEATH· own. I am not certain that the figures ERS Cartridge! would bear me out, but I received the dis tinct impression that there are more indi Get the NEW W·202·C Cortridge Set for your present vidual manufacturers of television and ra record player (automatic or manual to enjoy unex· dio in England than in the United States. I also noticed much heavier emphasis on celled .high fidelity reproduction). short- and long-wave receivers for use in the home, as well as equipment of all kinds built especially for certain climatic condi tions such as the tropics. I believe that portable and small table-model radio-pho nograph combinations are seen more today in England than in the United States-at least that is the impression that one gets For the ultimate in record reproduction, 'with at the Radio Show. There is a tremendous one grom stylus pressure, combine the stondord general interest on the part of the British W·202 Cartridge Set with the new WEATHERS W·12 public in the various products of the Brit W·12 or W-16 Reproducer Arm. Reproducer Arm ish radio industry. It would appear to me that a great deal could be gained by both sides in our indus Change to the WEATHERS Cartridge NOW and p r. eserve try if there were more visits across the At your records for the years to come. lantic in both directions. While I think our British cousins could probably profit by WEATHERS INDUSTRIES seeing some of our trade shows. I also _ strongly feel that ,we have quite a lot to Box 531 66 E. Gloucester Pike learn from· them when it comes to putting Barrington, N . J. on an exhibition such as the Radio Show. AUDIO ENGINEERING • OCTOBER, 1952 81 CONVENTION PROGRAM NEW! [Cont·it/ued frolll page 58J Here Is Audio's finest Cabinetry THURSDAY, October 30 (cont'd) 2:00 p.m ...... Technical Session INTERMODULATION DISTOR TION SYMPOSIUM INTERMODULATION MEASUREMENTS, H . H. Scott, Her'mon Hosmer Scott, Inc. MEASUREMENT OF NON- LINEAR DISTORTION, Alan Bloch, A ll-dio Instmment Company, Inc. The COMPARATIVE STUDY OF METHODS FOR The MEASURING NON-LINEAR DISTORTION IN SCHUBERT BARTOK BROADCASTING AUDIO FACILITIES, Dona ld E. Maxwell, Electrot~ics Laboratory, Gell eml E lectric Company Long known as the country's leading builder ' EXCLUSIVE DISTORTION IN PHONOGRAPH REPRODUCTION, of cabinets for custom-built TV receivers, River FEATURES H . E. Roys, RCA Victor DivisiOl~. Edge now presents a d istinguished seAes of • Speaker enclosures are horn enclosures for home music systems. loading type .qulpped with McProud·designed " Flex·O· D,istinctive in appearance-built to the high Port"-adj ustable to matcl! FRIDAY, October 31 standards of fine furniture-acoustically engi the speaker of your choice: 10:00 a.m ...... Technical Session neered by C. G. McProud-these new River • All cabinets made from the original spec ies of wood spe· Edge cabinets offer nO compromise with quality. clfied in the finish. SPEECH INPUT SYSTEMS Yet they are moderately priced. A vailable in • Heavy 13/ 16·lnch plywood a wide range of authentic styles. See them at Dsed throughout - corners mltro· locked and reinforced BASIC PROBLEMS IN AUDIO SYSTEMS PRAC y our nearby sound department. with blocks. TICE, VlT. Earl Stewart, RCA Victor Di See us in Room 504 at the Audio Fair! VISion AUDIO FREQUENCY INPUT CIRCUITS, Wil Write today liam B. Snow, Vitro Corporation of for handsomely RIVER EDGE INDUSTRIES America illustrated Ri ver Edg e . Ne w J ersey . ORadell 8·0900 ATTENUATOR TYPES AND THEIR. ApPLICA Brochure HR-2 N Y Showroom: 192 Le xington Av e . CHich ring 4·2120 TION, C h ester F. Scott, The Dave" Com pany THE DESIGN OF SPEECH INPUT CONSOLES FOR TELEVISION, Robert H. Tanner, Northern Electric Company, Ltd. 2 :00 p.m...... Technical Session DESIGN -DATA CONSIDERATION OF SOME FACTORS CONCERN ING THE USE OF AUDIO TRANSFORMERS, W . E. Lehnert, Audio Developmellt CompallY BYPASS AND DECOUPLING CIRCUITS IN AUDIO DESIGN, Lewis S. Goodfriend, Au,dio Instru1I/ent Company, Illc. R-C NETWORKS IN AMPLIFIER DESIGN, Edwin D. Sisson, Bell Sotttld Systems, Inc. ATTENUATION EQUALIZERS, F. R . Bies, Bell T elephone Laboratories, Inc. . NETWORK TRANSFORMATIONS, Leslie Norde, Hal1/1'1/G.1'I!l.1ld Manufactwring Company. SATURDAY, November 1 10:00 a.m ...... Technical Session HOME MUSIC SYSTEMS ANALYZING THE LP PICKUP PROBLEM, X302 Theodore Lindenberg, Pickering & CO l'll NEW Reel Extension Kit pany,IlIc. List $ 30.00 BINAURAL SOUND REPRODUCTION AT Hm.{E, Harold T. Sherman, Sherman St1tdio TESTING AND ADJUSTING SPEAKER INSTAL 10~" REEL ADAPTER attaches in 1 Minute LATIONS WITH THE SOUND-SURVEY METER, au Designed for standard N.,A..B. reels. Converts Pentron William R. Thurston, Gel~eral Radio recorder and players . . . doubles normal playillg Company time for professional needs. Reel adapter can also be used for smaller size reels without detaching from CONCERT HALL REALISM THROUGH THE recorder or player. USE OF A DYNAMIC LEVEL CONTROL, John Nigro, Madison Radio SOlmd, and Jerry THI: HNTRON CORPORATION 221-Ar E. Cullerton St.. Chicago 16, Ill. In Canada: Atlas Radio Corp .• Ltd .• Toronto B. Minter, Meamremellts CQrpora.tion. AUDIO ENGINEERING • OCTOBER, 1952 the only personal part of any ofajt minute J!eUer- ~ Magnetic Tape Presenting communication Sir : system! Mr. Latham's article, "Limitations of Magneti c T ape," (£, Sept. 1952), may ' be perfectly correct in what it says, but we are PHAN·TONE inclined to take obj ection to its implica STRAIN-SENSITIVE tions and to what was left unsaid. PICKUPS After checking into the matter, it ap pears that Mr. Latham's article was writ PHAN-WOOD ten some time ago when pre-selected tapes for instrumentation applicati ons were not TONEARM commercially availabl e. H owever, during in the the delay in getting the article cleared for publication, considerable progress has been luxurious setting made with improved tapes. Minnesota of Mining has been extremely cooperative and has manufactured special tapes for instru ARROW mentation uses for over a year. Contrary ELECTRONICS' to hi s article, therefore, such tapes are not unavailabl e and the price is not excessive. New dynamic Many laboratories are now usi ng mag under·ch;n TEL· netic tape recorders for data analysis. It EX Dyna ..t , wi th more highs and woul d appear that any budget that pre low s of both music designed to M~dern, lighlwefghl, cludes the spending of a few extra dollars and speech, is the de- durable . . . Easily to purchase pre-selected tape for this pur COMPLETELY light of radio and TV man· pose would nullify its entire usefulnes s. adiuslable and built itars. Weighs only 1.25 oz. demonstrate for hard usage, Maintaining an opposite view would be TElEX Headsels give t------r(P.~. analogous to purchasing a Cadillac and SOUND then complaining that it does not deliver tap qualily reception in its natural wilhout the punish. 'TWINSET peak performance because one cannot afford ( ment of exIra weight This lightweighl to purchase premium-type gasoline. setting 1.6 oz . TE L EX and pressure. You are cordially invited to attend our Twinset pipes si g demonstration of a new Ampex 0 to lOO-kc Off ice Transcribing nal d irectly into PFANSTIEHL the ear, blocking recorder at the forthcoming Audio Fair. Machines • Rojio out ground noises Improved recording techniques ' will be CHEMICAL Mpni toring • Tel e· and banishing listen· shown and various tapes will be used for costing ._ Amat eur ing fatigue. Magnetic. C,QMPANY ! i di rect comparison studies. . Ra dio . Record Stores I ______.... III~:;I!~~ Kenneth B. Boothe, WAUKECAN, ILLINOIS • Th eaters . Phone· r Director, Instrumentation Di vision , Order Boards .Wired Audio & Video Products Corporation, - Music Ins tallations 'EARSET New York, N. Y. • Commercial Com Sensitive munications • EI TELEX Earset sl ips onto ear Iro nic laboratories. and is pceferred · Talex produce. by all who use single'phone head' ".oJ,." ;0 sets. Weighs only t/2 manufacturers' oz . and leaves other ear free Presenting specification. for phone calls or conver solion. POSITIONS OPEN and AVAILABLE 'Trade Mark Slandard af den~en the World for PERSONNEL may be listed here at no charge to industry or to members of Quality the Society. For insertion in this col For complete information on any of the umn, brief announcements should be in LOUDSPEAKER abo.e headsets, write the hands of the Secretary, Audio En EQUIPMENT TELEX gineering Society, P. O. Box 12, Old ELECTRO-ACOUSTtC for DIV., Department, 6-8 Chelsea Station, N, Y. 11, N. Y., before St. Paull, Minnesota the fifth of the month preceding the HIGH FIDELITY SOUND In Canada date of issue. ATLAS RADIO CORP., iC Positions Open • Positions Wanted in the Toronlo * Sales EngIneer. Technically skilled a nd luxurious setting experien ced m a n wanted by The A udio Exch a nge. Selling a bility desira ble. Must of j ustify g ood salary. The Audio Excha nge, IMITATED 159-19 H illside Ave., J a m a ica 32, N. Y. ARROW hut not OL 8-0445. ELECTRONICS' EqUALLED ~ AudJo Laboratory Development Engl. n eer, communications background, famil ia r wit h adva nced deSign a nd measure ment of electronic cir cu its, components, networks, etc. Ma n w it h initia tive a nd rieJt{J4oad * orig inality capa ble of a na lysis fr om f un damentals to get practical r esults ex designed to TO-300 peditiou sly. Som e familia rity w ith elec THE WORLD'S FINEST tr o-acou st ics desira ble. Excellen t oppor COMPLETELY tunity for right m a n t o build up dev elop demonstrate OUTPUT TRANSFORMER m ent staff in growing company. Sm a ll This unique and superior transformer is friendly organization, countt-y-life sur designed for use in Ultra-Linear* cir SOUND cuits. On exhibit in Room 542 at the roundings. Salary comm en surate \Vith in its n a tural Audio Fair. Available at lea AUDIO ENGINEERING • OCTOBER, 1952 Ii Observations on Presenting V-M TRI-O-MATIC Demonstration Techniques RECORD CHANGERS AND HARRIE K. RICHARDSON ':: PHONOGRAPHS in the luxurious setting At home or in the showroom, audio equipment must be demon of strated properly if its capabilities are to be appreciated ARROW by the listener-whether a potential buyer ELECTRONICS' or ,merely the owner of the system. s THE MARKET for high-quality au Don:t Play the System Too Loud dio equipment has expanded to There is no question about extended Ainclude millions of music lovers designed to frequency l'esponse and low distortion COMPLETELY whose interest in the science of sound being the prime requisi tes of any good is strictly non-technical, there has be music system, but both qualities are nul demonstrate come increasingly apparent the need for lified if the gain control is cranked up SOUND improvement in demonstration tech to the extent that there is discomfort on nique. in its natural the part of the listener, Naturally, this Only a few short years ago, the aver setting level will vary with the individual, and age 'buyer of high-fidelity equipment as a consequence no hard and set rule was so engineeringish in character that can be established-however there are he was perfectly satisfied to select an a few points which can be accepted as amplifier simply on the strength of its a fairly safe guide. ability to cover a wide frequency range. First, forget all you have read about Frequently, an entire demonstration duplicating the full volume of a sym set-up consisted of nothing more nor phony orchestra in an average living less than an audio oscillator, the ampli room, 'Practically speaking, it can't be -:= :::;;;; fier in question, and a VU (pardon, it -...... J done-and even if you could do it you was 'db in those days) meter. On the wouldn't like it. Remember, in a concert Presenting strengtl1 of the meter's gyrations, the hall there is sufficient cubic volume to amplifier found a happy home or pro permit dissipation of the tremendous longed its stay on the dealer's shelf SOUNDMIRROR ( sound energy generated by a full sym ® { without uttering a single sound. phony orchestra and, if the hall is cor TAPE RECORDERS Those who bought audio equipment rect acoustically, there is a pleasing ra in the ways we speak of cared very little in the tio of direct to reflected sound which is J about music in an esthetic sense. So far luxu.rious setting quite apparent on well-made record as they were concerned, music was but J ings. of a necessary evil to be endured as a con To achieve identical reproduction of ARROW J cession to friends and neighbors who refused to share their enthusiasm for a symphony orchestta by electrical ELECTRONICS' J curves and characteristics, also to the means, your living room would have to local fire department which found no be as large as the auditorium in which • J amusement in the siren-like goings-on the live performance transpired-and ~ J of an oscillator feeding a lot of watts the walls would have to afford complete into a batch of speakers. absorption in order to avoid the effect designed to J Speaking in a literal sense, them days of the room's own acoustical qualities. I COMPLETELY is gone forever. Figuratively, though, Naturally, such idealized conditions are J their influence remains, as is evidenced I beyond the realm of probability. demonstrate by the antiquated demonstration tech Where small groups-such as string II niques which still prevail in the show I SOUND quartets, or soloists-are concerned, you rooms of many less-advanced dealers may well attempt to duplicate the full in its natural and jobbers. Also not entirely guiltless level of the live performance. Such com , ( of retarding the entlmsiasm of audio's binations sound best when they are newly found apostles are thousands of !!letting I heard in fairly intimate surroundings I{ hi-fi bugs who evaluate a music system small public dining rooms, for example ) ) THE BRUSH purely on the strength of how high and -many of which approximate in size how low it will go and, more impor an average sound demonstration room. DEVELOPMENT CO. tantly, how loud it will 'play. This brings Here the fact that the physical dimen CLfYELA ND. 0\-\\0 us to the cardinal sin of most demon sions of the two rooms are nearly the strations. same-both being ideally suited ~or listening to a small chamber group-tn- \II Associate Editor , AUDIO ENGINEERING. AUDIO ENGINEERING • OCTOBER, 1952 / dicates that the sound level of the elec everything from d.c. to d. flat within strator, use them to clinch your sales; trical reproduction may well equal that zero db, yet is apparently oblivious to remember, the person entering your of the live performance with enjoyable the fact that the resultant sound could sound studio for the first time is there results. stand a good shot of chlorophyll-when to find out for himself if high-quality When music is heard thwugh a high all he has to do to correct the situation audio will give him the same fine music quality audio system, it is most pleasant is touch a tone control. he has heard in the llomes of friends. when it is reproduced at a level which In most modern input signals The answer is to let him hear music as delivers to the listener's ears the same whether from a pickup or a tuner-the he likes to hear it-and generous use of magnitude of sound pressure that he weakness lies in linearity, caused by the tone controls provides the means. would receive at the original live per individualities of recordings and broad * * * formance. This is not to say that the cast stations. In other words, the wanted The points mentioned are paramount a, ct~tal sownd! level of the original per frequencies are in the signal all right, among those which govern the success formance must be duplicated-but that but not in the proper proportion to or the undoing of any demonstration of the effect of the performance can be meet your listening desires. Well-de a home music system, and they are those recreated if the sound output of the mu signed tone controls are capable of com which are most frequently abused. sic system is adjusted in keeping with pensating for even the most pronounced There are many other items which bear physical surroundings. case of too much or too little bass or heavily on this subject, and which may To the best of the writer's knowledge, treble-of making the incoming signal be covered in subsequent approaches there has been no complete research meet your standard of what the music such as choice of program material, covering this entire question. Personal should sound like, which is not neces avoidance of worn or scratched records, experience, however, indicates that the sarily that of the broadcast or recording etc. The big thing to remember is that relationship which exists between the e,ngineer. thousands of newcomers who are ap sound level of a live performance and Only through the use of tone controls proaching the audio field for the first that of the reproduction should closely can you be certain of achieving the re time are interested in music and music approximate the relationship which ex sponse that suits you, irrespective of in alone. The method of its achievement is ists between the cubic volume of the put signal quality. If you are a music entirely incidental. All you have to do hall in which the live performance oc lover, make liberal use of your tone is playa record and make it sound the curred and that of the room in which controls to add to the enjoyment of way it sho1t.ld-and you've sold a bill of the reproduction takes place. your music system. If you are a demon- goods. One thing is certain beyond all doubt -when music is reproduced under cir cumstances which do not permit the same degree of sound energy dissipa tion, relatively speaking, as that which prevailed at the original performance, there will be lacking the very quality of naturalness you are striving to attain. Don't Be Afraid to Use Tone Controls It has long been a mystery to me why there is such reluctance on the part of audio hobbyists and sound equipment demonstrators alike to make use of tone controls. The contn)ls on a modern high-quality amplifier are precision de vices in every respect-designed to com pensate for the frequency deficiencies of incoming broadcast signals or record ings. Yet, from the way these useful little devices are shunned by many dem onstrators, you'd think their only func THE WILLIAMSON AMPLIFIER tion was to mask shortcomings of the amplifier itself . . The first production model endorsed and signed by the designer Recordings-even those of the same manufacturer-vary in quality all over the lot. Even though careful control is D.~. N.CU;t~. maintained over every technical opera tion, pick-up conditions differ, to say SPECIFICATIONS • Output: 15 watt peak, 12 wart undistorced, nothing of the likes and dislikes of vari within 0.2 db from 10 cis to 20,000 cI s; har monic distortion at full output within 0.1 %; ous conductors and recording engineers. noise level herter than 90 db below fuIJ oucpuc. • Output Impedances: Choice of J, 4, 9, 16 2S. A good case in point is the London 36, 49 and 64 ohms by series/ parallel arr~nge. Montovani record which is enjoying menU of 8 secondary windings. so matching, without losses, a wide diversity of speakt'r such popularity at present. combinations. • Tube Complemenr: Two 6SN7, two KT66, Audio characteristics of broadcast one SV4 recdfier. stations, too, seem to vary more in keep Construction: The power and amplifier units are on separate chassis 12"L. 51//'\V. 6J.4; "H . ing with personalities than with tech All filrer condensers are oil tilled paper. Trans formers and chokes are specially wound and at ~ nicalities. In the New York area there screened in matching compound filled steel caSes. are at least a dozen FM stations on the Has OUtpUt socket for supplyjep f'9"'t;" IP ~ air, each of which could be recognized Price $159.00 net in U.S.A.- control unit, Adju5ca ble bali/prjJ}K ; OnlNI, and DEALER ENQUIRIES INVITED mett'r ln g Jack s a l'e f't.l ~Qd . A ll h.cki' 10 ... <1 k-tck .,l. by its audio quality, even though its call aff of s~andard A'!1encan type. Replacements of letters were never mentioned. Engineered in England to precise standards, U.S~~~CHlllY machtned parts a r C! ava1\ .... b le in the: this Amplifier is an integrated design and In the face of all this, it is difficult to gives a guaranteed performance with re understand the audio fan or demonstra liability and consistency. tQ; who mentions a dozen times per '" Prius for Canada and SOlllb & Cenlral mInute tha t his amplifier is reproducing America on reqllesl, AUDIO ENGINEER INC • OCTOBER, 1952 B£St \N SOUND FAIR PREVIEW always in Stock at [from page 60] RE'GIBTEREO TRADE MARK features which are certain to popularize it SOLDERING HUDSON with architects and builders. As in previous years, Hermon Hosmer INSTRUMENTS Scott, Inc., will attract both professional engineers and music lovers with a showing ·Any Voltage Range Supplied from 6/7 to 230/250 volts. of fine equipment ranging from sound meas Our instruments for 110 volts uring devices to high-quality amplifiers. are superb in making This will be the initial public display of Scott's new Type 420-A Sound Analyzer, SOUND an advanced version of the famous 41O-B JOINTS Sound Level Meter. for all Waveforms, Inc., also will offer a display of dual interest - including the minature SOUND Model 51O-B audio oscillator for engineers, EQUIPMENT and the new Model A-20-6 amplifier for Supplied to leading British Engineered music lovers. electrical manufacturers and Although Fairchild Recording Equipment H.M. and foreign govern Corporation is planning to display a com ment departments. the Most plete line of recording and playback equip- from Your These soldering instruments are named instruments as Speaker they are such a complete departure in design from usual solder bolt or iran are ideal for all modern assembly and maintenance work on telecommunica tions, radar, television, wire- less, etc. 3/16" dia. bit Standard Models 3/1 6" Detachable Bit Type (Factory Bench Line) • Heating time: 90 seconds • Consumption : 25 watts ment, interest of observers is expected to • Weight: 4 ozs. focus on the improved Fairchild miniature • High temperature • Handle unaffected by element dynamic cartridge. temperature • Length of instrument: 9" 15"...... $85.00 * * * • Equally suitable for daily or 15"...... $80.00 There you have it-a wee peek into some intermittent use • Prices of the enchanting exhibits which are being Standard 3/1 6" Bit Model $3.15 planned to make your visit to the 1952 Standard 1/ 4" Bit Model 3.50 Audio Fair both interesting and enjoyable. Detachable 3/1 6" Bit Model 4.20 Schedule of the Fair is as foIlows: Wednes Catalogue sent free on request. day, October 29, 10 a.m. to 9 p.m.; Thurs MADE IN ENGLAND day, October 30, 10 a.m. to 6 p.m. ; Friday, 1{e~~istered Design (U.S.A., British, &. Foreign Patents) October 31, 10 a.m. to 10 p.m.; Saturday, Write direct to sole manufacturers November 1, 10 a.m. to 5 p.m. and suppliers: Whether you are an engineer, a music lover, or a dealer-so long as you have an ADCOLA PRODUCTS, LTD. interest in audio-the Fair offers you four CRANMER COURT fabulous days you will never forget. The CLAPHAM HIGH STREET Audio Fair is YOUR affair - so BE LONDON, S.W. 4, ENGLAND THERE! ---Circle 6-4060..., r.r;-wrsr48th Sf.. 212 FULTON ST. I J Ne w Yo rk 36. N. Y. (Dept. 0-10) New York 7. N. Y. r 10 Please send FREE copy of 1953 Hud~on Catalog ~ \ E tl c \ Q S e~ Is 0 ~M C k 0 M.O. ~ "". : : .". ::::: : :: : : : : : : : : .. :.""".", aD Ship the follOWin g: ...... I I ...... · ...... ··...... ·· .. .. · ...... ··· ...... ··.... ··" I \ ~\~\ \\\,\,\\\\\\\\\\\\\\,\\\\\\\\\\\\ "'\\\\\\\\"""""u,...... '\ ,,~\\\\\H""h\"' . ,\\11' 11 11\1\\\\\\\\\\\1\\1\1 .. \ 1~'\1 1\\\\\\\\\\\\\\\1111\11\1 ~\ \\" ,,\\!\I \ """::J ~~\ 1\ . ~ \1\11\ fI'!!!" ~ 1111111111'1'" 11\111\ ~----~~ ,~~-~ ------~--~ - -- NEW LITERATURE ~--:::--- • Minia t ure Precision Bea rings, Inc., Keene, N . H. gives complete specificatipns on more t han 1'20 d ifferent types a n d SIzes CONGRATULATIONS of m in iatur e ball bearings in Catalog 52B, ) now available on request. Althou gh only to 4 pages in s ize, t his p u blication is a Vir t ua l necessity to designers and manufac ) ) t u rers of aviation instrU1l1ents, calneras, ARROW Ideal for indicating and recording mechanisms, and I other precision equ ipment where weight, BROADCASTING space, and f r iction problems are pre )) ELECTRONICS' ) RECORDING sented. I PUBLIC ADDRESS • Dow Corning Corporation, Midla n d, Mich. has prepared a thorou ghly interest I ) I~ : ) liThe ultimate in micro ing- 32 -page book on Dow Corn mg 200 phone q ua/ity," says F luid, the simp lest of a ll t h e s ilicones. Ev a n Rushing, sound The product's remarkable versatility has I I on creating I ) engineer of the Hotel resu lted in many misu nd erstandings as to New Yorker. the nature of the fl uid itself-all of w hic h II will be cleared up by this book lists a ll I I a n ew ) • Sh oul right Into the properties from boiling poin t to sound new Amperite Micro. t ransmission . A most worthw hile p ub li and II phone-or stand 2 feet cation if your in terest lies in the field of I I ) away-reproduction fs s ilicones. inspiring II a/ways perfect. • Triad Transformer Manufa cutrlng Co., • Not affected by P.O. Box 178 13, L os Angeles 34, Calif., any climatic condilions. lists more t h an 450 items with specifica way' to tion s a nd prices in Catalog TR-52. In I I I • Guaranleed to with. cluded are hermetically -sealed transform stand severe "knocking ers designed to MIL-T -27 specs, high demonstrate around." q ua lity a u dio transformer s, 400-cycle power transformers, toroids, geoph ysical I transformers, and amplifier kits. Copy will be mailed on r equest. ) • Keithley Instruments, 3868 Carnegie Ave., Cleveland 15, Ohio, is r el easing a I TELEVISION CHASSIS 2-page folder d escribing t he company's new Model 109 electronic wattmeter. Con TV AND AUDIO KITS I ( tained in t h e bulletin are d et a iled descrip I I tion, specifications, a nd suggest ed u ses, includ ing tran sformer core loss and cop TECH -MASTER per loss tests, measu r ing a udio power to I speakers, and power measu rements at PRODUCTS aircraft frequencies. I • Precisi on Paper Tube Company, 2035 W. ) 443 BROADWAY Cha rleston St., C h ica~o 47, Ill. has p u b lished a new arbor lIst in catalog for m, NEW YORK, N. Y. in w h ich a r e d escribed mor e t h a n 1500 s izes and s hapes of t ub ing available on regular or der. The 16-page boolclet w ill b e mai.led on requ est to industrial u ser s. • Lenlturt Electric Co., 1131 County Road, San Carlos , Calif. d escribes the properties of a w ide r a n ge of hig h "Q" tor oida l in • ductors in Bulletin T L -P 4. I ncluded in the listings are " Q " c u rves of t h e variou s coils as well as r epresen tative standard values. Ind u ctan ce values r ange f r om 1 m h to 80 h, alld tolerance is within 1 per cen t. Copy will be mailed on request. • Gib s on E lectric Company, 83 12 F ranks f town Ave., Pit t sburg h 21, P a . d escribes properties a nd u ses of t h e compan y's line - Functional of electrical con tacts in a new, well-pre pared l"2 -pa ge cata log. Of par ticula r value TON[ARM! to e ng ineers is a discu ssion of various a l SPEAKERS Design loys, a nd a section devoted to t h e selection of con tacts for variou s applications. Y our in the I'equest s hould specify Catalog C- 520. luxurious setting • Federal Telephone and Badio Corpo Discover the hidd en music ration, 100 K ingsla nd Road, Clif t on, N. J. of in records- untap p e d by has produced a sound and color m otion stand ard phonograp h eq uip- picture titled " Modern Communication s ment. U se a good turntable , let w it h Microwave" w hic h is availa ble for ARROW the PFAN-WOOD TONEARM com pa n y personnel and g r ou p s h owin gs. with a Strain-Sensitive Pickup* Described graphically and con vincin g ly ELECTRONICS' is t he de velop ment of micr owave r a dio bring out the best in 'your records r elay a nd its applications In mod ern day -old and new. iT'.dustry. In preparing t h is fi lm Fed eral .J Near Perfect Tracking gives friction has presen te.d the electr on ics in dustr y free la t eral, vertica l motion. w it h a vital ser vice, for w hich t h e com nany deserves grea t commenda tion. The " Adjustable Needle Pressure, Trackin·g fi lm is 16 mm and r uns for 20 minu tes. Angle. . TJ'q u iries sh ould be addr essed to Film " Different Woods dampen resona nces, Distribu ting Department. If you d on't see designed to pre vent t ransfer of vertical, hori this you are r eally m issing somethin g . zontal vibrations. • BAceiving Tube Division, Baytheon COMPLETELY " Adjustable Height and Vertica l Align- Manufacturing Company, 55 Chapel St., demonstrate ment. Newton 58, M>tss. a nnou nces s ix new s u bminiatur e tubes in a booklet w hich is PFAN-WOOD TONEA RM is equ ipped for t h e now available for distribution. Inclu ded SOUND PFAN - ToNE Stra in-Se n s i t ive Pic kup. >tmong the new t u be types are a d ua l in its natural *Ad'a p ters a vailable to use o the r pickups. d iod e, t hree d~J a l t r iodes. a voltage r eg-u l>ttor tube, a n d a vo lt ~ g-e refere nce tuhe. Ask y our r a dio supply m a n or write t od ay F.ssontial interest in this book lies w ith setting for FREE INFORMATION. d"~ i gn engin eers. Requ ests should be addressed to T flc hn ic>t l Information Ser vice, Specia l Tube Section. PERM·OFLUX CORP. • CaUfone Cornor ation. 1041 N. Sycamore Ave., Hollywood 38. Calif. is n ow r ele>tsin g p~ a new 8-page 2-cnlol' c>ttalog which illus tr~ . t.es and descri bes the company's new CHICACO 39, lLUNOIS 104 lake View Ave nue Waukegan, Ill inois 1953 p or table phonographs, tr>tn scrlption N O W READY- GENUINE PFANSTIEHL REPLACE players, and sound systems. Mailed with MENT NEEDLES tipped with Patented M47B Alloy each catalog is a combined sP{! cification fo r all popular car'ridges. ' and price s h eet. AUDIO ENGINEER ING • OCTOBER, 1952 87 pipes in the same way has less effect on the reed pipes. The reeds may there SOUND HANDBOOK fore seem to go sharp or fl at as a group [contimled from page 37] when the temperature changes. ITRON The reed organ stops are used to TI-SPEED create the sharper timbres. In the older slightly towards that of the independent organs the reed was allowed to strike edge tone, and the fi nal resultant fre 'RECORDER the aperture which released the air ql!lency is a compromise between the two, stl-eam, so that air current stoppage was with the air resonance very much pre CESSORIES both sudden and complete, and the upper dominant. The in fl uence of the edge tone, harmonics were very prominent. This however, cannot be disregarded. For produced a fi ery, almost savage tone example, the natural periods of the edge which may still be heard in certain re tone and of the air column in an organ cOl-dings. Most modern organs curve pipe must be similar in value, or a rela the end of the reed in such a way that tively long time will be required for the air jet is not cut off as suddenly, and energy to build up in the column vibra the tone is smoother. tion, and the pipe will not "speak" Ordinary organs produce fundamen promptly. (Adjustment of the pipe's tals clown to perhaps 30 cps, but a few edge-tone frequency is one of the prob have been built for subsonic fundamen lems of the "voicer.") Another example tals as low as 8 cps. of the influence of the natural frequency of the edge tone may be seen in the con trol of pitch which the flutist can exert by varying the intensity of his blowing. UND T he resonant frequencies of an air column, as we have seen, depend upon natural its effective length rather than its physi cal length, and the end correction, a ting function of the diameter of the pipe, also varies with the order of harmonic. The NTRON pipe is thus slightly mistuned fo r some at the harmonic overtoiles, producing a RATION discordant note. This effect may be I ULLERTON counteracted by using a narrow pipe with a much smaller end correction, or 16, ILL. by sup-pressing the higher-order har monics in the pipe and using separate pipes with high-frequency fundamentals to inject the desired overtone di rectly. The resonant frequency of an air column is dependent on the speed of sound in the enclosed medium. Since this speed varies with the temperature it Fig. 5-3. Eddies formed at the lip of an organ nting is important that the flu e pipes of an pipe. The original photographs were taken by organ are not distributed over parts of a mixing fine smoke with the air. (Courtesy Joumal de Physique. ) building which are likely to maintain temperatures different from one another. The flute and its higher-pitched sister, A change of 20° F ahrenheit will in the piccolo, work in a similar way to the crease the general pitch about half a flue organ pipe. In the former instru semitone. In this connection it is in ments the edge tone is created by blow teresting to note that in certain types ing transversely across the blow hole, of organ pipes the primary sound gen and the exciting stimulus for all fre fIDELITY erator is a reed. The vib ration of the quencies must be produced at the same WIER mechanical reed is not nearly as much lip. The effective length of the air col a slave to the air colunID as is the edge umn is varied by opening holes in the tone, with the result that a rise in tem tube through a system of levers and perature which affects all of the flu e keys. "V,Then the player "over blows" he designed to COMPLETELY delDonstrate §ODND in its natural Betting 88 AUDIO ENGINEERING • OCTOBER, 1952 raises the edge tone in fundamental fre New Lile lor High Fitlelity quency so that it meshes with a har- anti Paging Systems Fig. 5-4. Oscillograms of wave farms produced by a flute blown p (top), mf '(middle), and f (bottom). (Courtesy Case Institute of Tech nology, from "The Sci ence of Musical Sounds," by Dayton C. Miller. monic mode of the air column resonance. The pitch thus jumps an octave on the The Model COB-16 Loudspeaker. first overblowing (since the second har Cast aluminum rectangular horn design results in monic has a frequency ratio to the fun an all -useful concentrated beam of sound 35· damental of two to one) " and a fifth on vertically and 100· horizontally, free from dis the second overblowing (the third har turbing reflections and echoes. Response 350 to 11,000 cyeres, continuous power rating 25 watts. monic has a frequencv' ratio to the sec Available in B, 15 or 45 ohms. For public address ond of three to two). use or as a mid-range speaker in three-way high fidelity speaker systems. Ample space provided The transverse flute is a very old for transformer where required. Flush mounted. musical instrument. In its primitive Dimensions 12%" W, 6" H, 10Vz" D. Buy it at your favorite sound distributor Or order form the player blew across the end of direct. Net price $3B.22. a hollow reed, and later holes were in Free catalog! troduced into the side of the reed to allow control of pitch. The immediate In Canada: precursor of the modern transverse flute Dominion Sound is the recorder, an instrument of the Equipments, 'lfaame~ amc. flute class whose edge tone is produced Ltd. S2 East 19th Street, New York 3, N. Y. by blowing into the pipe, through a whistle head, rather than across it. In the middle of the 19th century Theobald Boehm developed the flute key mecha nism and hole spacing which is used The air load today. The Boehm system has also been ing on the adapted to the clarinet and oboe. Super Horn :;'01' operates in Flutes may be made of hard wood, such a way brass, silver, or even gold. The material to in HIGH FIDELITY of the body of the instrument may affect crease acous its tone in two ways, by damping and tic damping in by resonant vibration. Figtwe 5-4 illus the speaker, h-ates the wave fo rms produced by a minimizing speaker hong over. This gives truer cleaner flute blown at different intensities. The f MIN'NEAPOLIS reproduction. Acoustical damping combined higher notes of the flute are of almost with a lock of tuned co.vities -gives non perfect sine-wave form. resonant response down to 40 cps, using Call Lincoln 8678 typical 12 inch speakers. Because the Gately Reed Woodwinds Super Horn is corner mounted, the walls and ELECTRONIC CENTER, INC. The clarinet, oboe (that "ill wind that floor become on actual port of the nobody blows good") and saxophone are speaker system. 107 Third Avenue North reed woodwinds. Like the reed organ Mahagany, 12" . $75.00 net pipe these instruments use a mechanical Mahogany, 15" .$80.00 net WE FEATURE: vibrator to generate their primary EitIJer model;s available in blonde finish at $5.00 exira. MciNTOSH sound. The reed may be single, as in the clarinet and saxophone, or double, as in RADIO CRAFTSMEN instruments of the oboe family. The lat r------, PICKERING ter group includes the bassoon and an ELECTRO-VOICE instrument with the misleading name of GARRARD English horn. Figure 5-5 shows the (an effect described by Bernoulli's Name'______~ ______~ theorem), forcing the passage to close; SEE US for tape recorders, the reduced air flow of the constricted Address,______tuners, amplifiers and kits. passage then allows the pressure to re turn to normal, and the reed springs City zone __Sfafe___ I back, inertia taking it beyond its nOf- L AUDIO ENGINEERING • OCTOBER, 1952 ---~~------IJ Pay LESS lor the BEST in Amplified Sound! Fig. 5-5. Characteristic wave form of an oboe playing mf, at middle C. (Courtesy of Case Insti tute of Technology, from "The Science of Musicil l Sounds," by Dayton C. Mi ll er.) mal pos ition. This cycl e of events is re several of its resonant modes. When the peated as long as the a ir stream is con player changes tension on his lips he can tinued, and the throttling action is force the fundamental frequency of the characterized by a saw-toothed wave vibrating "lip-reeds" to mesh with some form containing all of the harmonics. other resonant mode of the a ir column . The controlled air-column resonances and he therefore has command of a of the tube dominate the vibrati on fre limited number of pitches. More com quencies of 'the reed; the coupled system plex brass in struments allow the player creates a tone of the desired pitch and to change the length of the a ir COIUI1JI1- with a rich, expressive timbre. "Quack by adding di screte secti ons of pi pe ing" noises are produced by inexperi through a system of valves, as in t he enced players when the reed vibrati ons trumpet, F rench horn, and tuba, or by are allowed to esca)'le from their coupling sliding a telescopi c assembly of tubes in with the air column. and out, as in the trombone. It may be Brass Instruments seen that the folded horn used for loud speaker loading, in which a long, grad No need now to hit the top price T he mode of operation of various types uall y fl a ring horn is made to occupy a bracket for a full range, distortion of modern horns is illustrated by that of reasonable space, is deri ved from the free, radio-phono amplifier. Bell's the simplest, the bugle. The pl ayer's lips, design of brass in struments like the tuba. new Model 2200 gives amazing 'flex which are pressed again st the cup-shaped in whi ch a horn approximately 18 feet ibility in use ••• delivers 20 watts mouthpiece, serve as the primary gen long is coiled into a fairly convenient at less than .3 % distortion! Peak erator of alternating impluses, acting in shape. power is 35 watts. Here is superla a manner v.ery similar to the double reed. tive quality at a medil!m price for In botl'! reeds and brass the effecti ve the utmost in listening pleasure! The Bernoulli effect causes the lips to radiatin g- surface is increased by the throttle the breath being forced into the horn d e~ i g n . MASTERFUL CONTROL! l' ugle with a saw toothed peri odicity, and Five-position equalizer switch affords ideal Drums, triangles, cymbals, and like method for correcting recording character the folded air colullln is stimulated at in struments are essentially mass-elas- istics on all types of records. Seven inputs, including radio, crystal phono, two magnetic pickups, TV, tape, and microphone, are Fig. 5-6. Frequency selected by five-position switch. Bass and and amplitude varia treble controls are continuously variable, with flat center positions. Volume control tion in the voice of FREQUENCY is . compensated for low level listening. singer Arthur Kraft MAGICAL RESPONSE! performing a portion AMPLITUDE of "All Through the Frequency response plus or minus % db 20 to 20,000 cycles, with controls set for Night." Note that Oat response. Hum level 80 db below rated frequency vibrato is output. Unit has removable etched dial plate always present, but for console or custom installation, with six 1%" extension shafts furnished. Three AC that amplitude vi FREQUENCY convenience outlets on back of chassis permit brato is subdued and control of entire custom installation with and often absent. AMPLITUDE master power switch on the amplifier. (Cou rtesy University WRITE FOR NEW HIGH FIDELITY FOLDER of Iowa and Harold Seashore. ) -- ACTUAL TONE RANGE "'''',... ,- ACCOMPANYING NOISE RANGE '-CUT-OFF FREQUENCY OF FILTER DETECTABLE IN BO% OF TESTS BASS DRUM • SNARE DRUM I F YOU ARE MOVI NG TYMPANI~~~~~~n~mF~=~Hil~~!~rnE;l14' CYMBALS Please notify our Circulation De CELLO partment at least 5 weeks in ad PIANO vance. The Post Office does not VIOLIN forward magazines sent to wrong Fig. 5-7. Audible fre BASSBASSi~IOL~~~ TUBA quency range for TROMBONE IIIIIr destinations unless you pay addi FRENCH HORN tional postage, and we can NOT music, speech, and TRUMPET duplicate copies sent to you once. noise, after W. B. BASS SAXOPHONE- Snow. (Cou rtesy J. BASSOON - --- - To save yourself, us, and the Post BASS GLARINET-- Acous. Soc. Am.) CLARINET---- Office a headache, won't you please SOPR. SAXOPHONE cooperate? When notifying us, OBOE ------le ~§,~ give your old addre66 and FLUTE----- PICCOLO- --- p"~ U'" M..,.",• ."..Jt:I ... eQo . MALE SPEECH-- FEMALE SPEECH- Circulation Department FOOT STEPS -- • HAND CLAPPING- RADIO MAGAZINES, INC. KEY JINGLlNG- -- 40 100 500 1000 5000 I000020000 t'i1 \\\Qo \~ , \,{, '(. FREQUENCY IN C'I'CLES PER SECOND ~~~ ~~ O CTOBER, ' 952 , J:t,.\lt>\O ENG\NH.R\NG • ticitv devices which are shock excited by a sil1gle blow and then allowed to vibr~te of their OWll accord. Instruments lIke the kettle drum are tuned, producing a CONGRAiULATIONS ,4""'7~ note which may be varied by adjusting tension on the membrane. The triangle, to cymbal, and bass drum produce sounds HEADQUARTERS FOR whose harmonically unrelated partials2 ARROW are so diverse that no sensation of defi ELECTRONICS' SOUND EQUIPMENT nite pitch is created; the tone can only be identified as belonging to a general • • • • • • • • • • • • • • frequency area. "IN PERSON" REALISM The Human Voice Mechanism on creating · The human voice is produced in much IN YOUR OWN HOME a new when you choose from our the same way as is the sound of a reed instrument. The vocal cords, stimulated and LARGE SELECTION by a steady flow of air, from the lungs, • RECORD CHANCERS provide an initial vibration which is saw inspiring • SPEAKE'RS toothed in wave form. The resonating • AMPLIFIERS elements of the vocal cavities can then be way to • TAPE RECORDERS controll ed to pick off and reinforce vari • AM-FM TUNERS ous harmonics, giving the sound its tonal demonstrate structure. The crooner rejects the classical use of the full singing voice 'and substitutes a sort of moan, which is inadequate in intensity for a public performance, but of proper amplitude to serve as the input stimulus of a public-address system. The electronic assembly of microphone, am plifier, and loudspeaker may be con sidered as an intrinsic part of the crooner's acoustical mechanism. Intelligible speech is produced by varying the transient and frequency structure of successive sounds through changing the shape of the vocal cavities, especially of the mouth. The dependence of vOlVel identification upon frequency content is easily demonstrated; the vowel sound "ah," occurring on a phonograph record, may be changed to "aw" by decreasing the speed of the turntable. Unvoiced consonants like the hiss of the sibilants do not involve the vocal cords. [lRRKSTA~ The Vibrato ARMS AND Instruments differ considerably in the type and degree of control given to the CARTRIDGES performer. Where the player has con tinuous and immediate control of pitch help make , and amplitude he can introduce a musical ARROW effect called vibmto. T hi s consists of periodic variations, primarily of pitch ELECTRONICS, ' but also of amplitude, subsonic in fre quency, which enhance the musical value of the tone. Figu.re 5-6 illustrates the ~ frequency and amplitude vibrato used by a concert singer. The "tremolo" stops COMPLETELY ort organs provide a mechanically pro equipped to duced vibrato. demonstrate Frequency Ranges Directional characteristics of the SOUND ' acoustical lens at 50PO cycles. Figure 5-7 is a chart of the audible frequency ranges of various sounds. It in its natural The new Jim Lansing acoustical lens gives the highs a smoothness your ear will appreciate in is of interest to note that the theory of stantly! The new lens, a natural development discord referred to in an earlier chapter, setting brought about by the inadequacies of the multi cellular horn. distributes sound constantly and based upon the beat effect of non-coinci uniformly over the entire audio spectrum ... giv dent harmonics, is supported by the fact ing the highs a smoothness impossible to match PACIFIC by any other method. tflat certain chords may sound acceptable Drop into your high nQe't\~ de-..le r and ask for when performed upon instruments with TRANSD UC~R the full story today. li~ited overtones, but become intolerabfy discordant when sounded by other in COR', first in fine sound ~tru~l e nt s with strong harmonics extend "'_'t%~ ll1g 1I1to the higher orders. JAMES B. LANSING SOUND, INC. 2439 fletcher Dr~ Los An,geles 39.. ColiFomlD 2 A partial ' , A UDIO EN GINEERINC • t?6WJ'pYet- SOIlU/ aDy 8Jmp/e C01J1jJOJJeJ)j oJII OCTOBER, 1952 5 and 6 were made by using the circuit shown in Fig. 7 and adjusting the decade CLEAN BASS resistance box until the voltage drop [contimted from page 29] across it equalled the voltage across the good horn design. The second, designed speaker, thus indicating impedance di for IS-in. speakers has a taper rate to rectly. Figure 5 shows the impedance give a cutoff of 70 cps and has an effec curve of the same speaker in a well tive mouth area of approximately 2500 padded enclosed box of 4 cu. ft. volume sq. in., again satisfying the above re Note that the resonance has been raised MAGNASYNC quirements. to 61 cps, or 20 per cent. Figure 6 PENTRON Figure 4 shows the impedance vs. shows the impedance curve of the same PRESTO speaker in the Super H orn designed for REVERE frequency curve of a G.E. S1201D SOUNDMIRROR speaker mounted in an infinite baffle. 12-in. speakers. Note that the resonant STENO The bass resonance of this combination frequency of the speaker has been re SCRIBE is 54 cps. This curve and that of Figs. duced to 38 cps, or 27 per cent below WEB-COR infinite baffle mounting, or 40 per cent WILCOX-GAY below that obtained in a totally en closed box of the same approximate volume. Nearly a full octave has been added to the clean reproduction. This lowering of the resonant frequency shows that the air loading on the speaker is increased more than three times in the 40-cps region and even more at higher frequencies. Note the reduced amplitude of the resonant peak. This shows how the acoustical damping is in creased. It has been observed that radiation from the horn drops off rapidly below the cutoff frequency, but some frontal radiation from the cone of the speaker reinforces the lower frequencies and ex tends the reproduction. The acoustic Ty loading is maintained down in to the 40-cps region and acts as an acoustic damping on the cone, greatly improving .~ the transient response and power hand 3-5545 _1 ling ability of the system. Early experimental work with this de sign indicated that if the best possible reproducer were to be constructed, then RUSHING ANOTHER Fig. 2. Cross section of Super Horn through certain steps would have to be taken SHIPMENT OF FINE plane A-A of Fig. 1. Circled numbe rs indicate to eliminate panel vibration. The sides panel references in text and front panel are made of :Y4 -in. ply LECfRO-VOICE SOUND wood. The internal panels 1 and 2 are made of % -in. plywood, and these panels PROOUC'S fO ARROW act as additional bracing for the sides. A spline or bone is run down the back £LECfRONICS' LUXURY at the intersection of the sides to give additional bracing, and to act as a back AUDIO CENIER U leg. The ultimate test of any reproducer is how it sounds. W hen using live tape as source material, a good speaker and an Ultra Linear amplifier, the illusion of presence with the Super Horn is amaz Fig. 3. Cross section of horn through plane B-B ing. Organ music moves up and. down NOTE REDUCTIO ~3D OF BASS ;J: -' o RESONANCE ./ Fig. 6. Impedance TO 38 CPS ~20 curve of GE 5-1201 0 III i-' speaker mechanism in u ~ "Z. ;' Super Horn . of . '. . V S iO .' "V'- .-f-- ~ ! OF" J- -- \ \ \\\\':' '\ \ \ '. '. ,.... 1 \ • \ ' 'QOQf"~R SECONO , \' \ \tJl c~ \ ~ c~c\.<.s ) . , the scale and fundamentals are clearly reproduced. Bass transients, e.g. kettle drums, have a cleanness which only an untuned and highly damped reproducer can ~ive. Plucked strings and the tym- 'O~~++~---r-rt+HtH-~~-rrH~~ j t- R~O~~NCE. z30 ; . -" "-1- ~20~~~~---r-r~H+H--1-1-b~~--1 !,o~~~++~~~~~~~~~~~-bHK~--1 t- 1-- - o~ . 10000 _ . 100 ' .. I'R£(lU[HCY ,'" C YCLf:S ""R SECOND Fig. 4. Impedance curve for GE S-1201 D speaker mechanism in true infinite baffle. COMPLETE 15" A high·fidelity WITH receiver with a flat NETWORK frequency response of 20.20,000 cps, ± 2 db. Has self· contained power 'O'r-rt++~---r-r++tHH-~~-+rH~~ supply for use on 117 Y, 60 C. 8 tubes ~ I-m~CE plus rectifier. 2-stoge amplifier with boss 630 and treble tone control circuits and phone I input compensator. Power consumption: " 50 W. Size: 141f4W, 7 1/4 H, 8112D • ...... ,.. I 100 10lI0 NEW FR[OU£NCT IN CYCLES "EA SECOND PILOT Impedance curve of speaker of Fig. 4 AA 901 in enclosed box. A high.fidel ity amplifier power stage for use with the PA 911 or the AF 821. Fre· SOOn. quency response 20·20,000 flat within :::':: 1 db. Speaker output 8 and 16 ohms. Totol harmonic distortion less than .1% a t AT THE FAIR 10 Walls output. Uses KT66 power tubes. THE K ARI,SON ASSOCIATES p?'csent DECADE RESISTANCE BOX The Karlson Speaker Enclosure GEN . RADIO 1432J for BALLANTINE Ultra-FideUty S oundReproduction VTVM-3tOA This new basic acoustic diS_!!J coyery, the exponential slot Fig. 7. Circuit used to make impedance radiator, provides full range re- measurements. production with clean flat bass For use with the AA 901 . External appearance Has tone correcting volume control. Full from 25 cps up, res ulting in a of the Gately Super bass and treble controls, with flat posi new standard of music repro- Horn. tions at center setting of control knobs. duction, music you can FEEL. Separate mike input control to superim pose voice on radio, TV or phono. Circuit Simulated " point source" provides wide pani are easily separated. The smooth specially compensated for records made angle d i~ per s ion filling room with sound, ness of response and lack of tuning g ive to Am erican and foreign standards. allowing enclosure to be placed anywhere the bass viols a rich full sound, and rid in the room, and eliminating bass delay time them of the Johnny-one-note sawing See and hear this new equipment of horns and ported boxes. "Liveness" due in our complete audio studio. to greatly reduced distortion and true re sound associated with some other types Take advantage of the liberal sponse to even the weakest transients. of enclosures. The excellent coupling be TERMINAL TRADE-IN PLAN Higher outputs due to increased cone load tween the horn and the floor gives the on old standard brand equipment ing. A high-frequency response without reproduction a presence not otherwise stridency. Cut for either 12" or 15" obtained. ~pen Thu rs day Evenings liII ~ P. M. coaxial speaker. Beautifully finished in Ample Free Parking oller 6. P.M. BIBLIOGRAPHY Mahogany or Blonde. Small: 34 y," x 22 y," / .,. . x 17"; under 6 cu ft inside! Price: $94.50. Harry F. Olson, Elements of Acoustical Available direct. Engineering, D. Van Nostrand Company, Inc. New York, 1940. For full information, write: Terminfl' J~I'£on A'MOciaiej Don 't Forget THE AUDIO FAIR I ltfJdlo Corp. [W 1379 EAST 15TH STRE ET . BROOKLYN 30, N. Y. Oct. 29, 30, 31, and Nov. 1 85 CORTLANDT ST., NEW YORK 7, N.Y • Pat. applied (or Hotel New Yorker, N. Y. • ' phone: WOrth 4 - 3311 AUDIO ENGINEERING • OCTOBER, 1952 93 '-CLASSIFIED- Rates : lOt!: per word per Inlertlon for noncomm lnlal advertlseml nts; 2S¢ per word for ,omml relal adYer· t isements. Rat .. art net, and no dlMounts will M allowed. Copy must bt accompanied by remlttantt '1 full, and mU lt reach the New York offill by th. I nt of t he month prece dlna the date .f luu•• Miscellaneous Radio, TV and 'l'HE AUDIO EXCHANGE, INC. buys ami sells quality high-fidelity sound systems and H I - F I SPEA K ER S Electronic Pa rts co mponents. Guaranteed used aud new equip For Foithful Concert Hall men t. Catalogue, Dept. AE. 159-19 Hillside CRE ST TR ANSFOR MER COR P.- Added 4 power traus Aye., Jamaica 32, N. Y. Telephone OL 8-0445. Realism in Your Own Home formers for capacitor·input filter circuits . . . 2 power transformers for reactor-input filter circu its ... 4 filament ALTEC LANSING transrormers .. . 4 filter reactors. . 2 universal audio FOR SALE: Jim Lansing 15-in. woofer. output transformers . . . 2 heavy-duty audio output $39; UTC LS-58 transformer, primary 1500 15" DUPLEX PM SPEAKER and 2500 ohms, multiple secondary. $15; A two way speaker system that transformers. DU ~10 N T LABO RATO RIES-Withdrew series of 5, Y2 Presto 9C turn table, two Liyiugston arms. properly bl ends high s with lows . defteciion yokes. $49; 42-in. black crackle steel cabinet, $20. Freq. res ponse: 30 to ·16,000 ERI E RE SI STO R CORP.- Added additional disc cerami co n Da"id H a n COCk, 70 W. 95th St., New York cyc les. Power rating: 30 watts. capacitance values . . . also series of 1500, 3000, and 25. =". Y. RIverside 9-5816. Network imp.: 16 ohm s. 6000 volt high-voltage ceramicons ••. series of standard Speaker di. : 15-3 / 16". Depth: printed circuits. {"SED SURPLUS audio and recordiug equip lI Ve n. Weigh t with network FEDE RA L TEL EP HO NE & RADIO CORP.- Rcduced pricc; men t. Some good buys. Write for list. M. E . 40 Ibs. on RG series of coaxial lead-In cables. Boyd. 903 Salmon Drive. Dallas, Texas. INDU STRI AL CO NDENSER CO RP.- Added new series of Mode l 49 Stabelex capacitors. 604B $140.00 KEIT H RADIO-Introduced 6 new IF transformers. 30% DISCOUNT ON ALL LP RECORDS! MORR OW RADI O MFG. CO . ~Added 3 generator filter Best mail order service in the country. All UNIVERSITY Cobra 12 ...... 27.00 chokes, GC -6, GC-10. and GC-20 at $3.75 net each. records brand new and guara nteed. Specializ UNIVERSITY 6201 Coaxial 25 W. 12", PM 45.00 SOL A ElECTRI C CO .-Deereased prices on 6 constant ing in Hi-Fi reco rds. Send for free catalog UNIVERSITY 6200 Wide Range 30 W. 12" . voltage transformers with harmonic flIter, and on 5 and literature. Southwest Record Sales. Dept. PM ...... 21.00 constant-voltage transformers. AE-1, 4710 Caroline, Houston 4, Texas. UN IVERSITY " DiHuslco ne" Ext. range . 30 THO RDARSON- ME ISS NER-Added audio Interstage trans- W. 8 ohm . 12" ...... 27.00 fo rmer T-20A19 at $2.46 net. . ELECTRO -VOICE Radak Super-12. 25 W.. . 54.00 UTAH RADIO PRODU CTS CO .- Added 4 filter choke, 4 W.E. 755A SPEAKER in R-J 8-in. enclosure. JE NS EN G- 610 Tr iaxial. 35 watts ...... 229.50 vertical outP1lt. 2 vertical block ing oscillator, 4 power. practically new, $39. Stromberg-Carlson AR-37 GENERAL EL ECTRIC S1201D 25 watt. 12" 9 audio output, and 2 line transformers. phono amplifier, with bass, treble, loudness, PM ...... •..... 20.37 ;;"in, low-pass controls, $28. Alexauder Shaw. 152-25 163rd St., Flnshing, N. Y. FU LL RANCE HI - FI Recording Equipment, Speakers, Amplifiers, Portable For Apartment Needles, Tape, etc .•. CUSTOM 30-WATT Williamson Amplifiers - Dual Chassis, Peerless S-265-Q and R-560-A Small Home or Traveling ARG OS PR ODU CTS CO.- Added model PC-lA, record t,·ansformers, all oil-filled coupling and filter REK-O-KUT "Recitalist" changer carrying case, and S- and 12-in. corner bass capacitors; extra power takeoll'. Wt. 50 lbs., Exceptionally hi -fid elity 3 -speed f.efl ex bames models CB-8 and CB-12. Also the table $89.50. Dr. Nicely, Kenton, Ohio. model TV cabinets are now priced to include excise tax. phonograph. Plays records from 6" to BELL SO UND SYS TEMS, IN C.- Withdrew amplifiers 16" broadcast transcriptions. Repro PROFESSIONAL RECORDISTS also r e duces the full broad ra ng e of any 371SA, 3725A, 3750A , 3750A-R; mobile ampJilIer ql:lire a central agency for selling, buying, and recordin g at any listening level. 3723M; PA systems PA-3 715A, PA-3725A. PA-3750A; exchanging r ecording equipment. We are now Powerful spea ker is mo unted in phono PA system 2078; record player 2075; microphone DY-ll; and RC-47 recorder. pr eparing to fill this n eed. Write for catalog detach abl e cover of carryi ng case CRESTWOOD RECO RDE R CORP .- Added 3 models of PRO-1 which giYes detailed information on wit h 14 foot cord. Th e id eal "Magictape" recorders. profeSSional recording equipment only, or oll'er in strum ent for t he mu sic 'over DE C I METER , I NC .- Withdrew "professional" 'rv pre equipmen t for sale to who wants accurate undlstorted amplifier models 300 and 400. THE AUDIO EXCHANGE, I NC., reprodu ction . . • and does n't ELE CTROVOX-Added model W-52TPS, Mngnavox re 159- 19 Hillside Ave., Jamaica 32. N. Y. have space for a co nso le. I placement needle; reduced price of 6·oz. Aerosol can of OL 8-0445 RP -43C $229 .95 Stati-Clean to $1.50 list. Enjoy HI-FI Recording Pleasure GOLDRI NG GRA MAPHONE , INC.- St,ylus modeis 260 and FOR SALE: Tuners-Craftsmen C10, ex 270 reduced to $1.50 net each. cellent condition, $105 ; Browning RJ -20. good Duo-Speed TAPE RECORDER JENSE N MFG. CO .- Increased price of Model P8-Q. 8-in. condition , $80. Amplifier-Masco MA-10HF, Alnico 5 PM concert speaker to $17.67 net. Added good condition, $35. Only certified check or PENTRON " Viking" loudspeaker Model 69J10 at $4.28 net, for mouey order accepted. Ralph Ashworth, Chari nntnmotive repJa rements. ton City, Mass. Model9T3C MillER MFG . CO .- Diamond styli added for Astatic cartridges (7) . ror Electro-Yoice (1). ror Phllco (4), Compl,t, with crys and for Webster-Electric cartridges (3). A_ NOUNCING A NEW SERVICE-High tal mi ke, 600 ft. OXF ORD ElECTR IC CO RP.- Added 5PillS, 5PBMS. est quality discs cut from your tapes. All re.1 of plastiC t ape $134 50 5PCl\ 96 THE 5 E ARE THE WHY '~JJII.A 1ST H: E LEAD E R 1 NTH E AU D 1·0 A T TEN U A TOR FIE L D FOR HEARING AIDS ... VEST POCKET R ~DIOS • • • MIDGET DEVICES UTe Sub-Guncer units fulfill an essential requ irement for miniaturized components hav Ing relatively high effi ciency and wide frequency res 9nse. Through the use of special nickel iron core mate rials and wind i .•g method s, I hese miniature un its have per formance and dependability characte ristics far superior to any other comparable items. They are idea l for hearing aids , miniature radios , an d other types of I mi niature electronic equipment. The co ils employ au tomatic layer wi ndings of double Form ex wire . • . in a molded Nylon bobbin. All inSUlation is of cellulose acetate. Four inch color code d fl exible leads are employe d, securely anchore d mechanically. No mount ing facilities are provided , since th is would preclude ma ximum fl exi bility in location. Units are va cuum Impregnated an d double (wate r pro of) sea ed Th e curves below indicate L the excellent frequency response available. Al ternate curves are show. to ind icate operating ch arac - ". t eristics in va rious typical applications. ) D.C. List Type Application level Pri. Imp. In Pri. Se c. Imp . Pri. Res . Sec. Res. Price SUBOUNCER UNIT Input + 4 V.U. 200 a I 250 ,000 16 2650 $ 6.50 Dim ens io ns .. .. 9/16" x SIS" x 7/ S" 50 62,500 Weight .....~ ...... 03 lb. SO -2 Interstage / 3: 1 + 4 V U. 10,000 a 90,000 225 I S50 6.50 ' SO-3 Pl ate to line -+ 20 V U. 10.,000 3 mil 200 1300 30 6.50 25, 000 1.5 mil. 500 SO-4 Output + 20 V.U. 30,000 1.0 mi l. 50 lS00 4.3 6.50 SO -5 Reacto r 50 HY at 1 mil. D.C. 3000 ohms D.C. Res. 5.50 SO-6 Output + 20 V U "'100,000 .5 mil. 60 3250 3.S 1; .50 ' Impe dance ratio is fixed, 1250 :1 for SO-I, 1 : 50~f":'or:"':""SC::0-:_ 3,,". ""7..:.::..c;.::..:':"""Any impedc-ance=--;- betC--wee n -:7=:"':"'t he value--s s"-:;=hown ---'= ma, be employed. UTC Sub-SubOuncer units have exce ptionally high efficiency and frequ ency ran ge in thei r Ultra-miniature size. Thi s has bee n effecte d through the use of specially selected Hiperm-A lloy co, ~ ma terial and speCial Win ding methods. The cons truction al details are Identical to those of thr Sub-Oun cer units described above. The curves below sh ow actual characte ristics under typi cal conditions of appl ication . Ii.c. List ,' Type Application leve l Pri. Imp. in Pri. Sec. Imp. Pri. Res . Sec . Res. Pr-jce · SSO ·l Input + 4 V.U. 200 a 250 ,000 13.5 3700 $6.50 50 62 ,500 SS O-2 Interstage/3: 1 + 4 V.U. 10,000 a 90 ,000 750 3250 6.50 Pla te to line + 20 V.U. 10,000 3 mil. 200 2600 35 6.50 25,000 1.5 mil. 500 + 20 V.U. , 30,000 1.0 mi l. 50 ~ 8 75 4.6 6.50 50 HY at 1 mil. D.C. 4400 ohms D C. Res. j.50 + 20 V.U. I 100,000 .5 mil. 60 4700 3.3 6.50 1250:1 for SSO-I , 1:50 for SSO-:3'. Any im pedance between the values shown